298 J- Beard 



however, do bearings on the question, for it is only a bypothesis 

 that they represent rudimentary oviducts in the male. It is even 

 less of a presumption in favour of hermaphroditism, than the per- 

 sistence of a trace of a Müllerian duct in the males of some Verte- 

 brates. These ducts are eiliated, as stated by Nansen (6 pag. 58, 

 also pag. 59) and they open into the body-cavity. 



They have since been described by myself as representing 

 nephridia, a conclusion which has been confirmed by Wheeler, 

 who has given a description of them in several species of Myzostoma. 

 One can hardly conceive any other possibility than that they are 

 the nephridia. Often they contain ova in the hermaphrodites, and 

 as often spermatozoa or sperm-mother-cells. In the males they are 

 well developed and eiliated. The part of the body, into which they 

 open, is, as will be seeu, a true coelomic cavity. In the males their 

 function can only be an excretory one. 



The body-cavity and the.developmeiit of the sexual orgaus. 



Previous to the appearance of Wheeler's recent memoir a body- 

 cavity had not been described in any of the 80 — 90 known species 

 of Myzostoma, Nansen and myself had, however, considered the 

 space in which the sexual products ripen as probably the remains 

 of a ccelom. 



If exceedingly young individuals be taken lor investigation — 

 specimens which can just be seen with the naked eye — sections 

 reveal the presence of a true body-cavity. The same fact can also 

 be made out in many of the hermaphrodite forms of tab. 2. 



The youngest individuai examined measured, including the 

 extended proboscis, about 0,2 mm. In section the ectoderm is a 

 simple layer of cells, which has, even in earlier stages, secreted a 

 fairly thick cuticle. Below lies the (at this stage) massive foun- 

 dation of the ventral nerve-cord, and, to the right and left of this, 

 the sacs of the sette. In the centre is seen the wide alimentary 

 tube, covered with a peritoneum. A contiuuation of this peritoneum 

 lines the inner dorsal aspect of the body-wall. Above and lateral 

 to the alimentary canal a space is seen, wich represents the body- 

 cavity. As Wheeler has already noted, in individuals of this size 

 the alimentary ca3ca are not yet formed. 



Some of the forms comprised in the two tables show the presence 

 of a body-cavity much more distinctly — at least on the haemal 



