on The Sexual Organization of the Rhizocephala. 



oportunity of tracing their genesis or development, but it is possible that they give a clue 

 to the question of the complemental males in the other Rhizocephala. 



These bodies are figured on Plate S figs. 14 rf, 18, and 19, and their position relatively 

 to the other parts of the body is shown in Text fig. 24. I have examined them in two spe- 

 cimens of Duplorbis by means of serial sections; in one specimen two bodies were present, 

 one at each end of the mantle-cavity, while in the other specimen I could only observe one, 

 but it is possible that I missed the other owing to the imperfection of this specimen. The 

 possibly paired regularity of their position speaks against their being complemental males, but 

 their relation to the other parts of the body, namely as two sacs invested by chitin and lying 

 attached to the internal chitinous investment of the mantle -cavity among the eggs, discon- 

 tinuous from the other tissues of the parasite, speaks in favour of this interpretation. Besides 

 their thick chitinous coat (Plate S fig. 18 ch) they consist simply of cells in process of sper- 

 matogenesis, the ripe spermatozoa being identical in appearance with those of other Rhizo- 

 cephala (fig. 19). The large cells with conspicuous nucleoli, which I interpret as sperma- 

 togonia, are very similar in appearance to the ''embryonic cells'' we have described in the 

 degenerate males of Sacculina: it appears tome possible therefore that these bodies are derived 

 from functional males which have succeeded in passing their embryonic cells into the mantle-cavity 

 in the manner in which the Cypris larvae of Sacculina evidently attempt to do, and that certains 

 of these cells have secreted a chitinous coat while others have proceeded to form spermatozoa. 



If we compare these bodies with the complemental males of Scalpellum vulgare, a section 

 through one of which is given on Plate 8 fig. 20, we may be struck by the essential simi- 

 larity of the two, though the males of Scalpellum show a much higher grade of organization 

 in the presence of muscles and a rudimentary mantle mc . 



Supposing that these bodies in Duplorbis are really males and not very peculiarly situated 

 testes, this animal would be a female with functional dwarf males as is the case among Cirri- 

 pedes in Scalpellum ornatum and velutinum, Ibla quadrivalvis and the whole order of Abdominalia. 



5. The sexual nature of Sylon. 



We have now discussed the sexual nature of all the forms of Rhizocephala concerning 

 which evidence is forthcoming, except Xylan, the little known parasite of Hippolyte and allied 

 shrimps. 



As pointed out in Chapter 7, this animal was originally studied by Michael Saks (6), but 

 an accurate account of its anatomy was first given by Hoek 10). I have had the opportunity 

 through the kindness of Dr. H. J. Hansen of Kjobenhavn and of Professor D'Arcy Thompson 

 in Glasgow, of studying four specimens by means of serial sections, and I disagree with 

 Dr. Hoek's account in only one particular, but that is of fundamental importance and concerns 



