HEEMAPHRODITISM IN MOLLUSOA. 31 



represents the highest specialisation of the hermaphrodite 

 genital gland, is only found in the Anatinacea among Lamelli- 

 branchs, and in Ento concha among Gastropods. 



III. Physiological Evolution of Hermaphroditism in the 

 MoLLUscAN Individual. 



The hermaphroditism of molluscs is not, so to say, self- 

 suflScient; in other words, the eggs of one individual have to 

 be fertilised by the spermatozoa of another. 



Speaking generally, the two kinds of products are not ripe 

 at the same moment in the same individual : an interval of 

 greater or less duration separates the two periods of maturity 

 of the diflFerent sexual elements. 



Leuckart was the first to make known that in certain Opis- 

 thobranchiate Gastropods the period of male maturity precedes 

 that of female maturity (31), i.e. the hermaphroditism of these 

 forms is protandric. 



This protandry ought to be regarded as a general phenome- 

 non in Euthyneurous Gastropods. This is notoriously the 

 case in the Pulmonates (32), and it has been recognised in the 

 various Opisthobranchs which have been studied from this 

 point of view, viz. Lobiger (33), the Thecosomatous "Ptero- 

 pods," e.g. Clio striata (34), Cy mbulia (35), Desraopterus 

 (36) ; Nudibranchs, among which I have observed it in Eolis 

 and Elysia; and lastly I may add Clione limacina (Gym- 

 nosomata), in which I have noticed that individuals of a length 

 of 15 millimetres (or less) do not as yet show any ova in their 

 genital gland, but stages in the development of spermatozoa 

 only. 



Similarly in Entoconcha testicular capsules are only to 

 be observed in individuals in which the eggs are not yet well 

 developed (37). 



For Neomenia, among Amphineura, protandry is equally 

 probable (38). 



In Lamellibranchs no general statement can be made with 

 certainty. I have been unable to examine young individuals 



