ASSORTIVE MATING IN CHROMODORIS ZEBRA 279 



cerned in this discussion are in need of more complete treat- 

 ment; the evidence required for such treatment I hope to obtain 

 in the near future. On some points the evidence already se- 

 cured is, I believe, sufficiently clear. 



When two specimens of C. zebra have successfully copulated 

 they after a time wander apart and usually proceed each to de- 

 posit an egg mass. This does not invariably occur, since some- 

 times only one member of a couple will lay eggs, but it is by 

 far the more usual condition. There is here no evidence of 

 functional protandric hermaphroditism, as claimed by Orton 

 ('14 b, p. 324) for some small nudibranchs (Galvina) ; indeed, it 

 would seem improbable that protandry could coexist with assort- 

 ive mating, whatever be the relative rates at which the eggs and 

 sperm are originally matured. Active sperm was found in the 

 vas deferens of animals which contained well developed eggs, 

 as well as in some which had just deposited egg masses after con- 

 jugation, including certain small specimens (5 cms. long), as 

 well as some of average length, and some very large ones (18 

 cms. long). 



During the copulation of Chromodoris the exchange of sperm 

 is not simultaneous, but one individual first acts as a male, 

 then the other; so that if two conjugating specimens be arti- 

 ficially separated after they have been united for a short time, 

 it is frequently to be observed that sperm is flowing from the 

 short penis of one nudibranch, which had been inserted into the 

 vaginal orifice of the other. When conjugating specimens are 

 segregated in separate aquaria, it is found that in many in- 

 stances one nudibranch will deposit eggs, the other not; while 

 in still other cases both animals will deposit egg ribbons, al- 

 though one of these may be very imperfect and contain but a 

 few fertilized eggs. From such observations I draw the con- 

 clusion, that as a rule mutual fertilization takes place during 

 the conjugation of Chromodoris. This conclusion rests further 

 upon the continued observation of animals which had conju- 

 gated in aquaria and had subsequently wandered apart without 

 being in any way disturbed; in most instances two egg masses 

 were the result of such matings. 



