226 PSEUD0B0NELLIA, A NEW ECHTUROID GENUS, 



of the adjacent uterine openings. It is, however, quite likely 

 that the male may be protruded through the canal of the andrce- 

 cium and actually liberate sperms into the female apertures. 



W. Kellicott, in his Textbook of General Embryology (1914, 

 pp. 106-7), drew attention to a series of organisms showing 

 various grades between fully developed males and females on the 

 one hand, and a fully developed animal of only one sex, with its 

 partner more or less parasitic on, or in it, on the other hand; the 

 final stage being reached in hermaphrodite self-fertilising flat- 

 worms; in other words, the sex relationship may be followed 

 through successive stages of symbiosis and parasitism, and, 

 perhaps, incorporation of one sex in the other (hermaphroditism). 

 The series mentioned by Kellicott includes the following : — 

 Certain Cirripede species in which there is a diminutive comple- 

 mentary male living parasitically on the hermaphrodite form: 

 Bilharzia, in which the elongate female lives in a canal on the 

 ventral surface of the male which is wrapped partly round it; 

 the permanent fusion of two hermaphrodites (e.g., Diplozoon) in 

 such a way that the female duct of each becomes continuous with 

 the male canal of its partner; or the fusion of a male and a 

 female, e.g., the gape worm of poultry, Syngamus; while an 

 extreme type is to be found in another parasitic nematode, Tri- 

 chosomoides crassicauda where the female harbours one or more 

 males in its uterus. He goes on to state that one might say that 

 the true climax is reached in self-fertilising hermaphrodites. 



We think that two stages between the conditions found in the 

 last-mentioned two worms can be exemplified by Bunellia and 

 Pseudobonellia. In Trichosomoides, the males, though somewhat 

 degenerate, are provided with a definite alimentary canal ex- 

 tending from the anterior end to the anus. In Bonellia, how- 

 ever, the male is a ciliate, planarian-like parasite frequenting 

 the oesophagus or uterus (or, in one case, the ccelome) of the 

 female; but it has neither mouth nor anus, and its alimentary 

 canal exhibits various degrees of atrophy. In other words, 

 parasitism has gone further than in the case of the nematode. 

 In Pseudobonellia, as we have already seen, degeneracy has pro- 

 ceeded still further, and the male is little more than a sperm- 



