A Contribut. to the Einbryol., Life-histoiy, iind Classificat. to the Dicyemids. 43 



ment wer e progressing- simultaneoiisly in the sa me in- 

 dividuai. 



These individuals contained a centrai nucleus and as many para- 

 nuclei as Infusorigens. The few Nematogens present contained a very 

 small number of embryos, generally not more than two or three. A 

 considerable number of individuals containing only numerous scattered 

 g'erm-cells were noticed. 



It is not quite clear how these two cases are to be explained. It 

 appears to me extremely improbable that the two modes of development 

 were destined to be carried far enough to bring fully formed embryos 

 of both sorts together, since no such instances bave ever come to notice. 



It is almost certain that one form of development was soou to be 

 wholly superseded by the other. As I bave not succeeded in tìnding any 

 evidence that Nematogenic development is ever succeeded by Rhombo- 

 genic , I am led to suppose that the young infusoriform stages in these 

 two Dicyemids were of an abortive nature, destined to disappear either 

 by dissolution or by breaking up into separate cells. The only credible 

 supposition remainiug is , that the few already fully formed vermiform 

 embryos were soon to escape, and that reproduction was henceforth to 

 be purely Rhombogenic. This may be the correct view, but I bave found 

 nothing outside of these cases that appears to confimi it. In both of 

 these Dicyemids a considerable number of loose germ-cells of the ver- 

 mific class was found, and their presence is more easily reconciled with 

 the former Interpretation than with the latter. 



3. D. moschatum^ from Eledone moschata^ Mar. 12. I shall bere 

 describe several individuals , and first of ali two young Rhombogens 

 and a young Nematogen, and then two cases of transition. 



a. Rhombogen .45 mm long. The posterior two thirds of the 

 axial cell contained nothing ; in the anterior third were seen two large 

 free nuclei (one .016 mm in diam., the other .020 mm) , and between 

 them a distinct Infusorigeu and a single isolated germ-cell. The larger 

 cells in the peripheral layer of the Infusorigen measured .014 mm, the 

 average size of infusorific germ-cells. 



b. Rhombogen 1 mm long. A little more than one half of the 

 middle portion of the axial cell occupied by a centrai Infusorigen, pre- 

 ceded by a nucleus and seveu stages of development , and followed by 

 four infusorific germ-cells (.014 mm in diam.) and sixteen embryonic 

 stages. Behind ali carne another free nucleus. 



e. Nematogen 1.20 mm long. This was the only individuai found 

 that contained a vermiform embryo. The contents of the axial cell were 



