NOTES ON THE FEEE-LIVING NEMATODES. 475 



a substantial majority, and it may be useful to quote Maupas' 

 words as to the relative frequency of the three kinds of forms : 

 '' Les females non-hermaphrodites mais simplement unisexuees 

 sont egalement tres frequentes. II ne sufEsait, en effet, de 

 placer sovis le microscope une dizaine de femelles prises au 

 hasard pour en recontrer une ou deux nnisexuees. Les 

 femelles simplement unisexuees y sont meme plus nombreuses 

 que les males qui les fecondent sans difficulte. Eu resume, 

 chez cette espece les males encore relativement nonibreux 

 paraissent avoir conserve leur instinct sexual intact." 



It is evident that this species, conld it be re-discovered, 

 would form a most interesting- subject of study. A precise 

 investigation of the comparative frequency of females and 

 hermaphrodites, and in particular of the relative effects of 

 self- and cross-fertilisation on the sexual constitution of the 

 offspring, would prove of the utmost value. ^ 



(4) The Nature of Hermaphroditism in the 



Nematoda. 



The evidence that the hermaphrodites described by Maupas 

 and myself represent the females of bisexual species, in which 

 a part of the gonad has been given over to the formation of 

 spermatozoa, is, indeed, overwhelmingly strong. Hermaphro- 

 dites and females are identical in general anatomy, and the 

 arrangement and form of their gonads are strikingly similar. 

 Then, too, there exist a series of species showing the develop- 

 ment of hermaphroditism from small beginnings in species 

 where the ratio of fertilised eggs to unfertilised is very small, 

 until in Rhabditis gurneyi the number of spermatozoa is 

 almost equal to that of the eggs they are required to fertilise. 

 Lastly, there are, apparently, species like Rhabditis 

 viguieri which have not yet decided between bisexuality 

 and hermaphroditism, and present an assemblage of pure 



' In Diplogaster mauj)asi, though careful watch was kept only 

 one liermaplirodite was found which failed to develop spermatozoa (see 

 Table I, fifteenth generation). 



