24 SUMMARY OF CURRENT RESEARCHES RELATING TO 



for the first division had a number of representatives in palaeozoic times, 

 the second was abundant in secondary epochs, and the Stenoglossata are 

 common in tertiary strata. The author appends a somewhat detailed 

 table of affinities and classification. 



Development of Helix Waltoni.* — Drs. P. and F. Sarasin found 

 that Helix Waltoni is very abundant in Ceylon. The young are re- 

 markable for the long time that they remain in the egg, where two 

 larval organs — caudal vesicle and primitive kidney — developo to a con- 

 siderable size. The former is finally as much as \\ cm. long ; it is, 

 doubtless, as Gcgenbaur has suggested, the embryonic respiratory organ. 

 The primitive kidney is large enough to be seen, on dissection, with the 

 naked eye, and has the function of an embryonic renal organ. 



On some parts of the body-epithelium small bud-like structures, 

 which are found to be sensory, may be seen ; they consist of a small 

 number of large pyriform sensory cells with stiff processes, and are 

 inclosed by long supporting cells. The whole structure calls to mind 

 the lateral organs of Amphibia. The lateral organs found by Haller in 

 rhipidoglossate molluscs appear to be more diffuse ; the lateral organs 

 of Helix are regarded as larval organs. 



The rudiments of the central nervous system are laid down very 

 early ; before the tentacles are visible the cerebral ganglia appear as 

 rounded masses of cells, still connected with a well-marked thickening 

 of the epithelium of the sensory plates. When the cerebral mass is well 

 developed there appear on either side of the sensory plates two invagina- 

 tions, which grow out into long tubes with caecal widened ends ; these 

 the authors call the cerebral tubes. Later on a large lobe may be seen 

 on either side of the cerebral mass ; these, which have a different struc- 

 ture from the brain, may be called the accessory lobes ; the spaces in 

 them are nothing else than the cavities of the two csecal sacs of the 

 cerebral tubes ; later on the two spaces and the efferent duct disappear. 

 These observations will doubtless explain the discrepancies in different 

 accounts of the development of the brain of Mollusca ; the authors who 

 state that the brain is formed from an epithelial thickening have 

 probably examined early stages, while those who have described it as 

 arising by invagination have seen the later. 



The authors believe that these cerebral tubes are the homologues of 

 the olfactory organs of Annelids, described by Kleinenberg in Lopado- 

 rhynchus ; in Molluscs they do not permanently retain the character of 

 open tubes, but pass into the brain, of which they form the lobes. 



Morphology of the Heteropod Foot.f — Prof. C. Grobben gives a 

 critical account of the views of Huxley, Gegenbaur, Leuckart, Kay 

 Lankester, and others on this subject ; but brings forward nothing 

 which can be called new. The investigation shows that in connection 

 with the pelagic life, and the associated development of a swimming- 

 lobe upon the foot, the primitive Gasterojiod sole has degenerated into a 

 sucker-like structure, which in the Pterotracheidse forms a secondary sex 

 character through its absence in the female. With the shortening of the 

 foot-sole is connected the specialization of the portion bearing the oper- 

 culum, which forms the tail-like posterior part of the body, and whose 

 fin-like development is in relation to the pelagic life of the Heteropoda. 



* Zool. Anzeig., x. (1887) pp. 599-602. 



f Arbeit. Zool. Inst. Univ. Wien, vii. (1887) pp. 221-32 (1 fig.). 



