92 PECTINID^. 



difficulty taken off. Notwithstanding this property, I 

 frequently find a small crab [Porcellana longicornis) in 

 their nests, and not unfrequently an annelid (Polynoe), 

 but almost invariably a greenish gelatinous annelid. 

 This last kind I have noticed lying across the tentacles 

 of a large Lima, which seemed to be quite at its ease 

 and by no means incommoded by its neighbour. I 

 have frequently kept L. hians in captivity for many 

 months. I have now (January 1863) one which I took 

 in May last, and it looks in good health. It com- 

 menced building in a day or two after it was put into 

 the tank, and has ever since lived under its own roof, 

 adding from time to time to the size of its oblong nest. 

 This word (' nest ') is, in a wide sense, not inappro- 

 priate as applied to the mode of architecture ; but it 

 must not lead to the idea of incubation, with which the 

 structure seems in no way connected." I am indebted 

 also to Mr. Robertson for another important observa- 

 tion, viz. that he has seen some individuals of L. Mans 

 shedding blood-red ova, and others spermatozoa at the 

 same time, and that the flow of ova continued for about 

 fifteen minutes, and to all appearance in two streams. 

 This observation is of great value as regards the genera- 

 tive system of the Lamellibranch Mollusca; but we 

 must not overlook the possibility that each individual 

 may be of both sexes, although the period may vary for 

 the development of its organs — i. e. that it may be male 

 at one time and female at another, as is said to be the 

 case with Valvata and Ancylus among the freshwater 

 univalves. Or it may be analogous to what takes place 

 in certain flowering plants. Lobelia is hermaphrodite, 

 but usually sheds its pollen before the anther is pre- 

 pared to receive it, so that self-fertilization is seldom 

 effected, and the pollen of a neighbouring plant with the 



