NOTES ON THE FREE-f-I VIXG NEMATODES. 481 



of the testis only is used for the formation of spermatozoa, 

 and to prevent squandering- of the slender stock the matura- 

 tion of the speruiatozoM, is completed punctually just after 

 a brood of eo-o-s enters the mantle-cavity. 



Both the Ehizocephala and the Neinatoda, tlie two best cases 

 of self-fertilisation, show one advantage obtained by the 

 animal wliich adopts this method of reproduction, and that is 

 the need for a reduced number of spei-matozoa. In Saccu- 

 lina the economy has been effected by a special change, to be 

 looked upon in the light of an adaptation, but in Rhabditis 

 and Diplogaster, as we have seen, the small and markedly 

 insufficient quantity of spermatozoa shows a recent entrance 

 into the hermaphrodite condition, and only because every 

 spermatozoon fertilises an egg do these forms succeed in 

 maintaining themselves. 



In the Tunicata, a group in which hermaphroditism has 

 established itself completely, the ova ripen before the sperma- 

 tozoa, and cross-fertilisation appears to be general. In 

 Ciona ripe ova and spei-matozoa are found in the ducts at 

 the same time, and Castle^ found that if the products from 

 the same individual are mixed, as a rule fertilisation did not 

 occur. This result is so significant that it is not surprising 

 that the experiment slioidd have been repeated. Morgan^ 

 found some variation in the degree of self-sterility, but 

 generally endorsed Castle's results. In experiments which I 

 cari'ied out at Naples on the same tunicate in the early part 

 of 1906 (and in which every care was taken to avoid contami- 

 nation with foreign sperm), the eggs of an individual were 

 found to be as fertile with their own spermatozoa as with 

 those of other individuals, yielding in both cases nearly 100 

 per cent, of embryos. The pathological development which 

 Castle found characteristic of self-fertilised embryos did not 

 occur in my experiments. In conclusion, it seems possible 



' Castle, W. E., " The Early Embryology of Ciona intestiiuilis, '' 

 ' Bull. Mus. Conip. Zool.,' xxvii, 1896. 



- Morgan, T. H., ' Jom-n. Exp. Zool.,' i, 1904, p. 137, • Biol. Bull.," viii, 

 1905. 



