sitory monodermic stage is epiblastic in nature, and not hypoblastic, as Robinson will have it. The true hypoblast spreads out against its inner surface, much in the same way as Van Beneden has described it for the rabbit, Van Beneden and Julin for the bat, Heape for the mole, Selenka for the opossum, and the author for the shrew. This conversion of the monodermic into a didermic stage is, however, in Tupaja brought about in a stage when the dimensions of the blastocyst are yet exceedingly small. In conclusion the author pointed out that the early developmental stages here sketched have confirmed him in the conviction that in the formation of the mammalian blastocyst cænogenetic processes play a prominent part. It is by precocious segregation that cell-matter of epiblastic and of hypoblastic ancestry is arranged into a two-layered vesicle, whereas the really formative matter out of which the embryo will be built up is yet quiescent in the embryonic knob. This fact has made the mammalian blastocyst a very puzzling structure to comparative embryologists; and we can only come to a clear conception of its real nature if we are willing to acknowledge that the holoblastic segmentation of the mammalian ovum is something totally different from the holoblastic segmentation of very many invertebrates and of Amphioxus. Being an apparently palingenetic feature, it is all the more misleading. And we must not wonder that the later processes of mesoblast formation have been affected by the cænogenetic changes just alluded to which have come about in the very early stages. 2. On the Ancestry of the Chordata. By W. GARSTANG. 3. On the Structure of the Integument of Polyodon. 4. On the Vertebra of Amphisile. By W. E. COLlinge. DEPARTMENT OF BOTANY. 1. Two Irish Brown Algæ. By Professor T. JOHNSON. The author described the characters of Reinke's genus Pogotrichum, founded in 1892, and compared them with those of Litosiphon, founded in 1850 by Harvey. The recently discovered plurilocular sporangia of Litosiphon Laminaria, Harv., were described, and it was considered that the evidence afforded by their position and characters with the differences in the vegetative organs was sufficient to justify the continuance of Pogotrichum as a genus distinct from Litosiphon. Lantern slides, microscopic and other illustrations, were shown. 2. Some Chalk-forming and Chalk-destroying Algæ. The author exhibited and described the characters of a number of Corallinacea (chalk-forming red algæ) collected by him at different parts of the Irish coast during the past three years. Preparations were shown of chains of spermatia forming the antheridia in Lithophyllum (Melobesia) lichenoides, and attention was called to their possible mode of formation. Specimens (microscopic, &c.) of shellboring algae were shown and new features in their life-history and distribution described. Suggestions as to the relation of the carbonate of lime to the two groups were made and asked for. 3. On the Development of Cystocarp in Polisiphonia nigrescens. 4. An Exhibition of Algæ. By A. CHURCH, FRIDAY, AUGUST 10, The following Papers were read :— 1. On the Relations of Protoplasm. By Professor E. VAN BENEDen. 2. On the Periodic Variation in the Number of Chromosomes. 3. On Chlorophyll in Animals. DEPARTMENT OF ZOOLOGY. The following Papers were read :- 1. On the Origin and Morphological Signification of the Notochord. By Professor E. van Beneden. 2. On the Carpus of the Greenland Right-whale compared with those of Fin-whales. By Professor J. STRUTHERS, M.D., LL.D. In his preliminary notice in 1885 the author stated the general conclusion that he found diminution in the number of bones in the second carpal row from Hyperoodon to Mysticetus. The following further observations relate to the whalebone whales only. The species and number dissected were: two of Balana mysticetus, five of Balanoptera musculus, one of B. borealis, two of B. rostrata, and one of Megaptera longimana. Besides noting the surface grooves, horizontal sections were made, showing the lines of fibrous suture marking off the limits of the cartilages and bringing into view ossifications not seen on the surfaces. As the fibrous sutures uniting these flat-walled cartilages are so narrow and firm as to prevent movement, these cartilages must be regarded as individually functionless, and we are prepared to find differences between the species and variation among individuals of the same species. In regard to the first row of the three usual mammalian pro-carpals in Mysticetus the intermedium sends up a peak between the forearm bones, articulating with ulna as well as with radius, and the pisiform is widely separated from the ulnare, in both of these particulars contrasting with the finners. In the second row, instead of the usual four disto-carpals in mammals, Mysticetus has but one broad cartilage bone, supporting digits III. and II., and in part digit I. Digits IV. and V. are supported by the ulnare, digit V. in part resting on the ulna, so that, on the ulnar side, the ulnare represents the entire carpus. The ossifications in Mysticetus vary. In the 48-feet-long female, which may be reckoned adult or nearly so, the only bones ossified in the left carpus are the inter medium and ulnare, and largely so; in the right carpus an ossification occurs also in the disto-carpal, of medium size. The radiale is not ossified in either carpus. In the 35-feet-long male Mysticetus, in the right carpus (the left not obtained), three ossifications occur, but they are in the radiale, the intermedium, and disto-carpal, not in the ulnare. Moreover, in this two-thirds-grown Mysticetus the metacarpal of the pollex is fully ossified, while in the adult the pollex is entirely cartilaginous. In the finners, in the distal row, two cartilage bones, more or less ossified, occur normally, supporting the two greatest digits. In the 65-feet-long B. musculus these two are united into one bone, notches above and below and a groove on the surface indicating synostosis of two formerly separate bones. In three of the five B. musculus a disto-carpal was found supporting the inner of the four digits, cartilaginous in the 50-feet-long one and in the 60-feet-long one, and with a small ossification in the 651-feet-long one. In the 45-feet-long one there was no trace of this third disto-carpal, either bony or cartilaginous, nor was it present in the 36feet-long B. borealis, nor in either of the two adolescent B. rostrata. In the Megaptera, 40 feet long, the ulnare is a very broad bone, extending for over one-third of its breadth below the radius, thus occupying also the locality of an intermedium, and between it and the radiale occurs an undersized intermediate bone. These two latter form the entire carpus, as one row, between the radius and the massive radial metacarpal. Small ossifications occur in the radiale and in the ulnare to its ulnar side. The pisiform is, in the great finners, large and square-shaped; in B. rostrata, narrow and directed upwards; in Mysticetus, transversely elongated. Regarded by some as merely a sesamoid, it serves as a stretcher, giving breadth to this broad part of the limb, steadied by the flexor carpi ulnaris muscle, which the author has found to be present in all the cetacea he has dissected, whether whalebone or toothed. In the 60-feet-long B. musculus it had an ossification as large as a walnut. The pisiform may be said to be the only one of these bones adapted to serve a function. The mass of cartilage forming the carpus serves to give some low flexibility and elasticity at that part of the limb, like a piece of firm indiarubber in the middle of an oar; but the mapping into distinct cartilage bones, more or less ossified, in these whales can be explained only on the view of inheritance from some mainmal whose diarthrodially jointed carpal bones were adapted to allow of particular movements. 3. On the Species of Amphioxus. By J. W. KIRKALDY. I. Branchiostoma Lanceolatum (Costa). Distribution. Mediterranean Sea, English Channel, North Sea, Coast of Myotomes 45, 17, 9. Head region very small, snout fin not marked off from the dorsal fin. Tail fin long and shallow. III. Branchiostoma Belcheri (Gray). Distribution.-Borneo and Torres Straits, Australia. Gonads 25 pairs. Both metapleural folds die out behind the atriopore. Myotomes 37, 17, 10. Snout fin long. Caudal fin wide and short. IV. Branchiostoma Caribæum (Sundevall). Distribution.-East Coast of S. America, Gulf of Mexico, West Indies. Both metapleural folds die out behind the atriopore. VI. Heteropleuron Cultellum. Branchiostoma Cultellum (Willey). Distribution.-Torres Straits, Australia. Gonads 19, unpaired. Right metapleuron continuous with the caudal fin. Left metapleuron dies away behind the atriopore. Dorsal fin very high. Both metapleura meet at the anterior end of the pre-oral chamber, and are continuous with the snout fin. Oral hood far back, and with few cirri, of which two sets, about a median cirrus, are webbed. DEPARTMENT OF BOTANY. The following Papers were read : 1. On the Phylogenetic Position of the Chalazogamic Amentiferæ. The author reviewed the points of resemblance that obtained between the Cupuliferæ and the four chalazogamic genera, Alnus, Betula, Corylus, and Carpinus, and was led to the conclusion that, with the exception of the difference in the route of the pollen tube and the concomitant adaptations, no fundamental distinctions could be drawn between the chalazogamic and porogamic genera. The author also described and exhibited some abnormal inflorescences of Fagus sylvatica, Quercus Ilex, and Alnus glutinosa, and suggested atavism as their explanation. 2. On the Hygroscopic Dispersal of Fruits in certain Labiates. 3. On the Hybridisation of Orchids. By Dr. JAMES CLARK. SATURDAY, AUGUST 11. DEPARTMENT OF ZOOLOGY. The following Reports and Papers were read : 1. Interim Report on a Digest of the Observations on the Migration of Birds at Lighthouses.-See Reports, p. 348. 2. Report on the Legislative Protection of Wild Birds' Eggs. 3. Report on a Deep-sea Tow Net. 4. On Temperature as a Factor in the Distribution of Marine Animals. By Dr. O. MAAS. In the question of the influence of temperature on marine animals no sufficient distinction has been made hitherto between three classes of facts: 1. Between the animals of the Plankton, the Benthos, and the Nekton. The eurythermal animals cannot be appealed to in proof of anything regarding temperature. For the stenothermal the average temperature of a locality is of small zoogeographical value, while the extent of variation is the most important factor. The Nekton animals are more eurythermal; otherwise their power of swimming, which brings them into very different conditions of temperature, would be of no use to them. |