418 SUMMARY OF CURRENT RESEARCHES RELATING TO 



INVERTEBRATA. 



MoUusca. 

 7- Gastropoda. 



Embryology of Paludina vivipara.* — M. Popoff describes the early 

 ■stages of the growth of the ovum in histological detail. Both male and 

 female sex-cells are distinguished by the presence of chromidia ; in 

 Paludina as in HeUx these arise close to the nucleus and show an 

 intimate relation with the chromatin transformations going on in the 

 same. This favours the view that the chromidia arise from the nucleus. 

 The formation of chromidia is not marked in the first phase of growth ; 

 it is contemporaneous with the most marked cell activity, and is thus 

 in close connection with the regulating processes of the cell. The 

 " Xeben-kern " (idiosome, idiosome residue, etc.) and the pseudo- 

 chromosomes (archoplasm, etc.) in the male sex-cells of Helix pomatia 

 are only transition stages in the transformations of the chromidia 

 (mitochondria and chrondromites). In the final stage of sperm histo- 

 genesis a part of the chromidia is thrown off along with a little mass of 

 plasma. There is dimorphism of the spermatozoa ; there are oligo- 

 pyrene and eupyrene forms. The former are the more active, but their 

 respective functions have not been made out. 



Locomotion of Gastropods. f — R. Dubois and Fred Yles point out 

 that various interpretati(.»ns have been given of the creeping movements 

 of Gastropods. The locomotion has been referred to vibratile cilia on 

 the foot, to the flow of blood into the aivernous tissue of the foot, and 

 to the musculature of the foot. The authors have experimented with 

 Fissurella nei/lecta ; by elimination of the action of the cilia and the 

 erection due to inflow of blood, they show that the muscular action is 

 the only important factor. 



5. Lamellibranchiata. 



Petricola phoiadiformis in German Waters. | — C. Boettger has 

 found this Fholas-Mko American bivalve near Sylt, and between the 

 north Frisian Islands and the mainland. E. Wolf has also found 

 specimens near the east Frisian Islands. This is a very remarkable 

 instance of importation, for the only other known habitat is on the 

 other side of the Atlantic. 



Locomotion of Pectunculus glycymeris.§ — Fred Ties describes the 

 movements of this bivalve. It makes its way in the sand by a sort of 

 ploughing, the characteristic features being the antero-posterior oscilla- 

 tion of the shell, and the utilisation of a displacement of the centre of 

 gravity by means of the foot. It raises itself into a vertical position and 

 tumbles over and begins again. On a hard body there is probably a 

 true adhesion of the plantar surface of the foot. 



* Arch. Mikr. Auat., Ixx. (1907) pp. 43-129 (5 pis.). 



t Comptes Rendus, cxliv. (1907) pp. 658-9. 



t Zool. Auzeig., xxxi. No. 7 (197) pp. 268-70. 



§ Bull. Soc. Zool. France, xxxi. (1906) pp. 114-7 (5 figs.). 



