ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 59 



thuriaiis. He finds that the basis of each is a group of hexagonal 

 prismatic cells, arranged in a single layer. Four adjacent cells serve as 

 the centre of attraction for the calcareous molecules, and give rise to an 

 X-shaped corpuscle. The calcareous deposit next attacks the other 

 lateral walls of the four cells, but the bases of these always remain free 

 from any deposit ; the centre of each cell is occupied by the nucleus, 

 the presence of which explains the holes in these bodies. As the deposit 

 is most abundant along the crests of the hexagonal cells, the surface of 

 the corpuscle becomes ridged. These four cells the author proposes to 

 call the four fundamental cells of the corpuscle, and he applies the term 

 of fundamental calcareous corpuscle to the body which arises by the 

 calcification of the lateral walls of these four cells. This fundamental 

 form is common to all the species ; the differences seen in various forms 

 are due to the mode of calcification of the surrounding cells. 



Coelenterata. 



Morphology of Siphonophora.* — In continuation! of his studies on 

 this subject, Prof. 0. Chun describes the post-embryonic development of 

 Physalia. He has been able to undertake this investigation thanks to 

 the collections made on board the ' Vittore Pisani,' and he has been 

 fortunate enough to find specimens which connect the larva? described 

 in 1858 by Huxley with adult forms. In a larva of 5 mm. it was seen 

 that the lower third of the air-sac is converted by a circular constriction 

 into an air-funnel ; the polymorphous appendages of the trunk are 

 distinctly differentiated into two groups, one larger than the other. 

 There was no indication of the crest. In the later stages the air-sac 

 was more extensive, the. crest developed, and the appendages increased 

 in number. The air-sac traverses the cavity of the enlarged trunk in 

 an oblique direction, and in such a way that the funnel approaches, near 

 the anterior larger group of appendages, the wall of the body, where it 

 flattens out into a sharply circumscribed plate. This " air-plate " 

 consists of a single layer of ectodermal cylindrical epithelium, which 

 passes at the margin into the flattened epithelium of the inner wall of 

 the air-sac. This, though it has escaped the notice of all observers, 

 grows to a considerable size, and is homologous with the secoudary 

 ectoderm in the pneumatophore of the Physophoridae ; like it, it is the 

 organ for the secretion of the gas contained in the air-sac ; the great 

 development of the secondary ectoderm explains the rapid renewal of 

 the air in the bladder. 



The recognition of a structure homologous to the air-funnel makes it 

 possible to understand the pneumatophore of Physalia in all stages of 

 development. A line drawn from the centre of the air-plate through the 

 pore corresponds to the primary axis of the pneumatophore of the 

 Physophoridaa ; the asymmetry of the bladder of Physalia becomes 

 marked very early. 



The structure of the crest is more complicated than has been hitherto 

 supposed ; there is a longitudinal septum which divides it into two 

 halves ; with this tile-like septa become connected, which arise from 

 its free edge and overlie the transverse septa of the first and second 

 order, and extend as far as the air-umbrella. Notwithstanding the 

 great development of its musculature, by means of which the living 



* Zool. Anzeig., x. (1887) pp. 557-61, 574-7. f See this Journal, 1887, p. 970. 



