14 D. M0011E ON THE GENERATIVE PROCESSES 



ciliatfd young, when they are puffed out from the parent shell in 

 small quantities at a time. 



In the foregoing description of the generative gland of these 

 creatures, I have taken for granted that the sexes are united in 

 one individual ; that the gland with spermatozoa is only a prior 

 stage in the history of the gland with eggs and young. If these 

 creatures are of different sexes, of course I ought to have described 

 the male gland and female ovarium. It is impossible to prove that 

 I am right in any direct way. We cannot open a cockle, examine 

 the contents of its gland, and then keep it separate to allow it to 

 go on to perfection. One great difficulty in the way of these 

 investigations is the necessity of causing the death of the animal, 

 or so injuring it as to render it incapable of carrying out its 

 natural processes. I can only say that I have seen in the different 

 animals examined such a continuous series of steps, from the 

 presence of imperfect spermatozoa to the last stage of extruding 

 the young, that I personally believe I am right, and that I think 

 any one with sufficient patience, and using right methods, would 

 also convince himself that the description I have given is sub- 

 stantially correct. 



I should like to add a few general considerations which I think 

 have some weight in deciding the question. Those who advocate 

 the opposite theory to the one I have put before you ought 

 to furnish conclusive evidence of the discharge of spermatozoa 

 from the glands of these creatures. I have never seen any such 

 evidence, and personally I have never seen an animal in the 

 breeding season whose gland did not contain either spermatozoa, 

 eggs, or lame, and surely if it be held that the spermatozoa from 

 one animal impregnate the eggs in another, we ought, at the same 

 time we see eggs and larval forms, also to see in other animals 

 glands emptied of spermatozoa. I have never seen such. Then, 

 again, I think the mechanical difficulty is great. In none of these 

 creatures are the eggs discharged before impregnation. The cockle 

 and mussel are ovo-viviparous, and in the oyster (although it 

 retains the eggs in the layers of the Branchiae until fully de- 

 veloped, possibly thus affording an opportunity for impregnation) 

 such a provision is manifestly unneeded, as we may find eggs 

 in an early stage in the gland with spermatozoa in another 

 part. The confusion in studying the oyster, arising from the fact 

 that different portions of the same gland are in various stages of 



