INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. GOT 



tlieir otocysts formed by a.n iuvaginatiou of the ectoderm, wliilc 

 there is a delamination of the layer in the Pteropoda and aquatic 

 Pulmonata. 



The pedal ganglia, on the other hand, exhibit a remarkable con- 

 stancy in their mode of development ; they are always formed in the 

 midst of a pre-existing mesodermal tissue, and can, therefore, only bo 

 said to be indirectly ectodermal in origin. 



These general considerations lead to still wider generalizations ; 

 rejecting the view of Bobretzky that the mode of development must 

 be the same tliroughout any one phylum, M. Fol states his belief that 

 the identity of embryonic processes is not to be assumed but is to bo 

 demonstrated ; and, looking at all the facts, he comes to the conclu- 

 sion that the processes of invagination and of delamination may bo 

 derived from one another, and that they have not the importance 

 which is often attributed to them. 



Benal Glands. — The Pulmonato Gasteropoda are interesting as 

 being provided with a larval kidney, which among the Mollusca has 

 as yet been only observed in Paludina and in a marine Prosobranch ; 

 paired, it is evidently of the same category as the segmental organs of 

 the Vermes ; the permanent kidney is unilateral, it is never developed 

 along the median, but always on the side on which growth is predomi- 

 nant. The larval and permanent kidneys are very similar in structure, 

 but they differ from one another in the fact that the inner pore of the 

 larval kidney opens into the body-cavity, while that of the permanent 

 one opens into the pericardium ; this is not, however, a ditference of 

 prime importance. A more important question relates to the " typical " 

 presence of two pairs of renal glands in the Mollusca, but this is a 

 question which cannot yet be answered. 



General Homologies of the Larval Pulmonata. — The Pteropoda 

 appear to be those of the Cephalophora which have most completely 

 retained, in their larval stage, the velum so common among the Vermes ; 

 they, too, have the cerebral ganglia most directly derived from the 

 ectoderm. In these, and some other points, the Pulmonata are tho 

 most divergent of the Cephalophorous Mollusca. So far as tho 

 digestive tract is concerned, they are only remarkable for the great 

 quantity of dcutcrolccithin. The larval kidneys do not find their 

 representative in the larva) of tlic Annelids or of Pohjfjordius, but 

 the permanent pair (for paired they really are) completely corresponds 

 in position and structure to the excretory organs of tho Rotifera and 

 to the first pair in the larva of Polijgordius. 



It is impossible to compare tho moUuscan larva with a segmented 

 worm-larva ; they only correspond to the cephalic portion of the larva 

 of an Annelid, or to an entire Rotifer ; tho Mollusca aronot segmented 

 animals which have fused their metamercs, but thoy arc animals 

 whicli have remained simple. 



In conclusion, tho author points out how recent observations tend 

 to favour the re-establishment of the Vermes of Linnajus ; tho larval 

 form (Lovenian, vcligcr, trochoi)horc) can, with variations in form, bo 

 traced through " worms," Annelida, Bryozoa, Brachiopods, and even 

 EchinodcrniK, and tliese all form a phylum distinct from that of the 



