mVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 237 



The whole area on which the shell is formed probably has its origin 

 in the shell-gland, the depression of the latter becoming less and less 

 marked, and its cells spreading out, as it were, over the mantle area. 



As already mentioned, the supra-cesophageal ganglia arise from the 

 " Scheitelplatten " ; probably the infra-oesophageal ganglia are formed, 

 indirectly, from the same groups of cells. The eyes and otocysts are 

 shown to be ectodermal structures ; the tentacles also arise as offshoots 

 of ectoderm, into which, at a later period, a mesodermal core extends. 



The most anterior section of the alimentary canal, with the 

 odontophore, arises from the ectoderm ; the midgut, and its product 

 the hindgut, from the endoderm. The dorsal and ventral walls of 

 the midgut are formed of small cylinder cells, the lateral walls by 

 large globular " albumen-cells " — endoderm cells immensely enlarged 

 by the absorption of albumen. Towards the close of embryonic deve- 

 lopment, these latter undergo extensive subdivision, group themselves 

 into larger or smaller lobules, acquire a yellowish brown colour, and 

 form the rudiment of the liver. 



The permanent kidney is formed from a group of mesoblast cells 

 at the hinder end of the embryo ; these cells soon arrange themselves 

 into a curved tube consisting of three portions : — a ciliated segment, 

 probably opening into the pericardium ; a secreting segment containing 

 concretions ; and a discharging segment opening on the surface of the 

 body. 



The heart also, in all probability, arises from the mesoderm ; in 

 the earliest stages observed, it already consists of auricle and ventricle. 



The fate of a group of mesoderm cells, situated in the same region, 

 just posterior to the tentacles, was not made out. Eabl considers 

 that they are probably identical with the structure which is considered 

 by Ray Lankester, in Limnceus, as the foundation of the supra- 

 cesophageal ganglia, by Fol as that of the connective tissue. 



Space will not allow us to give an abstract of the general remarks 

 on the above observations with which Dr. Rabl concludes his paper. 



Methods. — Up to the 24-ccll stage, no treatment of any sort is 

 necessary, except for the purpose of observing the division of the 

 nuclei. For later stages, the albumin is removed, and the eggs treated 

 with 1 per cent, osmic acid until they acquire a brown colour, then 

 with carmine or picrocarmine, and then with a mixture of glycerine 

 1 part), absolute alcohol (1 part), and water (3 parts). They are 

 then examined in glycerine. With advanced embryos it is best to 

 harden with alcohol of very gradually increasing strength, before 

 staining. For sections, the embryos (which arc about ! mm. in 

 length), were embedded in a mixture of wax and oil on a slide. 



Molluscoida. 



New Fossil Polyzoa.* — The Rev. J. E. Tenison-Woods describes a 

 new genus allied to Gcmrllaria — where the cells are joined back to back 

 and all the pairs face the same way. In the new form, however, the 



* ' Jouni. nnd Proc. Roy. Soc. N. S. Wales,' xii. (1S79), p. 57 (2 figs, of u 

 plate). 



