194 SUMMARY OF CURRENT RESEARCHES RELATING TO 



this group belonging to the larvfe of various Gasteropods. He figures 

 a specimen from the collection of the Eev. E. B. Watson, in which 

 the "pullus" and the shell of the adult are both seen. The members 

 of the genus Sinisigera, as hitherto regarded, appear to be the pulli 

 of many and varied genera. It is possible that, driven far from shore 

 by currents or storms, they pass their existence as larval forms and 

 never attain maturity. If this is the correct explanation, we can 

 understand how it is that, though so numerous, they are so constant 

 in size, and how it is they are dredged in a dead state from great 

 dej)ths. 



Green Colour of Oysters.* — Additional investigations have served 

 to convince Mr. J. A. Ryder that the coloration is unquestionably due 

 to a staining of the blood-cells of the animal, and that the colouring 

 matter is either derived from without or else may be a hepatic 

 colouring principle, which through some derangement of the normal 

 metabolic processes of the animal, has been dissolved in the lympho- 

 hfemal fluids, and so been taken up by the blood-cells or haemato- 

 blasts and given them their peculiar colour. The hypothesis of 

 tinction in no way disj)oses the author to assign a less value to the 

 influence of the food, as the primary initiatory agency in efiecting a 

 staining of the internal ends of the cells which form the walls of the 

 hepatic follicles. In fact, in certain oysters most affected, the hepatic 

 follicles are most deeply stained internally. He has failed to prove 

 by spectroscoijic research that this substance is chlorophyll, and his 

 belief that it is chlorophyll at all, has been weakened by the fact that 

 specimens which had the liver dyed deep-green and were affected in 

 other pai'ts, have shown no disposition to part with their colouring 

 matter, although immersed in strong alcohol for months, during 

 which time it has been changed two or three times. Chlorophyll 

 would not be likely thus to retain its colour. 



The hypothesis of vegetable parasites has in the author's opinion 

 no foundation whatever. 



Sucker on the Fin of the Heteropods not a Sexual Character- 

 istic. f — The posterior margin of the " fin " of the three genera of 

 Heteropoda, Pterotrachcea, Firoloides, and Carinaria, bears a small 

 sucker-like body which many authors allege to be characteristic of the 

 male of the two former. 



This structure, Mr. J. W. Fewkes says, is sometimes found on 

 the fin of the female. Among a number of specimens of Pterotrachcea 

 coronata collected at Villa Franca, he found a perfect female with 

 this organ as well developed as in the males. He has also studied 

 specimens of Firoloides lesueurii in which ovaries were well developed 

 where the sucker was present. Most observers agree in saying that 

 Carinaria has the primal sucker in both sexes. 



This organ is probably not confined to either sex in the above- 

 mentioned genera. Morphologically it may be regarded as a 

 functionless organ, or the remnant of a structure which in those 



* Amer. Natural., xvii. (1883) pp. 86 8. 

 t Ibid., pp. 206-7. 



