amoYKj the Parasitic Isopoda. 255 



The oviduct, wliich is always ])rc.sent as well as the vas 

 deferens, is a wide tube o])cniug externally at the side of the 

 body, in the segment in front of that whieh bears the penis. 

 There are some remarkable facts connected with the openings 

 of the generative ducts, for which I must refer the reader to 

 my original paper. 



I have never found any spermatozoa in the oviduct, as 

 might have been anticipated if they had been introduced from 

 without; in the vas deferens, as I have said, they are almost 

 always present ; and it seems scarcely probable that this duct 

 has the function (without ])arallel in the animal kingdom) of 

 trans))orting the spermatozoa from without into the ovary. 



Before passing on to Mr. Moseley's objections, it may be 

 well to point out how closely similar in structure arc the male 

 organs of the animals I have described to those of Asellus 

 aquaticus, a unisexual Isopod which has been so well described 

 and figured by Prof. G. 0. Sars (Crust. d'Eau douce). 



In order to prove his point, Mr. Moseley is obliged to make 

 the supposition that the vas deferens and penis which I have 

 described are rudiraentaiy. That this is not the case seems to 

 me to be amply proved by the facts (1) that tlicy are quite as 

 large as those found among the unisexual forms, (2) that the 

 vas deferens is usually filled with spermatozoa, and (3) that 

 in a specimen in my possession the spermatozoa may be 

 seen in the act of escaping from the orifice of the penis. 



Another objection brought forward by Mr. ]\Ioseley is the 

 difficulty he experiences in understanding why spcrmatophorcs 

 should be formed in a self-impregnating animal. The ex- 

 planation which at once suggests itself is that the formation 

 of spermatopliores is so common amongst the Crustacea, 

 that it is highly probable that they occurred among the uni- 

 sexual ancestors of the parasitic Isopods, and that a tendency 

 to their formation was inherited by their hermaphrodite de- 

 scendants. Now, unless we can show that a s]5ermatophore 

 is a disadvantage to a self-impregnating animal, there is no 

 difficulty in imagining that their formation might be continued. 



The last objection brought forward by Mr. Moseley, founded 

 on the immobility of the spermatozoa, is somewhat startling. 

 He says " the immobility of the spermatozoa observed is a fact 

 quite as much in favour of their having been introduced for 

 some time and tired out, as freshly developed and functionally 

 active." Now it is well known that motile spermatozoa are of 

 veiy rare occuiTcncc among the Crustacea, being found, accord- 

 ing to Gegenbaur ('Anatomic Com])aree,' p. 426), only in the 

 Cirripedes. It seems that Mr. Moseley, in his anxiety to dis- 

 prove my results, has had recourse to an hypothesis, viz. that 



