A Contribut. to the Einbiyol., Life-history, and Classificat. of the Dicyeinids. ()] 



p. 399), there are two distiuct kinds of ova in Dinoplnlus ^ the smaller 

 of which develop into the extreniely small males , the larger , ìnto fe- 

 males. Precisely the same sexual differentiatiou oceurs in the siimmer 

 egg'S of Kotiters. Whether the differeuce betwen the two kinds of germ- 

 eells of the Infusorigen is oue of sex or of generation , is a questiou 

 which I cannot answer. The comparison before introduced between the 

 Dieyemids and the Orthonectidae does not reveal a resemblance suffi- 

 ciently close to serve as a guide in this matter. After the discovery of 

 two females in the Orthonectidae by Julin, the parallelism between the 

 evolutiouary cycles of these parasites and the Dieyemids appeared to 

 be complete, provided the Infusoriform could be regarded as a male. 

 So complete seemed the analogy in other respects , that Van Beneden 

 did not hesitate to adopt this view of the Infusoriform and to incorporate 

 it in the table of Classification appended to bis last paper (2) . 



While I see no insuperable objection to such an Interpretation, and 

 fuUy concede that the history of the contents of the urn, so far as known, 

 renders it plausible , still decisive evideuce is wanting , and the argu- 

 ment from analogy is far from being satisfactory. 



In neither of the two female forms described by Julin do we find 

 auythiug comparable with the Infusorigen, nor anythingat ali resembling 

 the transitional phenomena before stated. The »cylindrical female« pro- 

 duces males, and can not therefore be said to correspond to monogenie 

 Dieyemids which produce females, nor to diphygenic Dieyemids which 

 produce Infusorigens, or, — passiug the Infusorigens — females and In- 

 fusoriforms. The »fiat female« produces a dimorphous female progeny, 

 and cannot therefore be compared with diphj^genic Dieyemids, unless the 

 Infusoriforms are females ; nor with monogenie Dieyemids , unless the 

 offspring of the bitter be of two kinds. Some of the oflfspring become 

 monogenie , others diphygenic ; but it is by no means certain that this 

 distinction originates in a differeuce of individuals. There is nothing in 

 their origin and development, nor in their adult form or structure, which 

 authorizes the opinion that they are unlike. Stili it must be admitted 

 that monogenie and diphygenic individuals may be primarily distinct, 

 since we do not yet know what determines the germ-cells in one case 

 to develop into vermiform embryos, and in the other, into Infusorigens. 

 However this may be , the parallelism between the »cycle evolutif« of 

 the Orthonectidae and that of the Dieyemids is not sufficiently complete 

 to enable us to decide on the nature of the Infusoriform. 



