A Contribut. to the Einbryol., Life-liistory, and Classificat. of the Dicyemids. 49 



mere aggregation of indifferent cells completely destitnte of ali strnctural 

 imity? or, does it show, for at least a time. a higher degree of cohe- 

 rency and a greater uniformity in the arrangement of parts than conld 

 be supposed to exist among cells having no structural relation with one 

 auother? If the seeond question be answered affìrmatively. as I think 

 it must, a third question at once arises coneerning the degree of in- 

 dividuality exhibited by this body of cells. Ts it the individuality of 

 an organ , or of an independent organism '? Although there is stili ranch 

 room for doubt on this point , there is certainly good ground for think- 

 ing that the lufusorigen represents an individuality of a personal 

 order. Long before suspecting any analogy between the paranucleus and 

 a polar globule, I was struck with the dose resemblance of the lufusori- 

 gen to the Gastrula of the vermiform embryo. So nearly do they some- 

 tìmes agree, that only the size and the presence of a paranucleus enable 

 one to distinguish the one from the other. Before ascertaining the history 

 of the paranucleus , and before therefore it could be used as a guide in 

 this matter, I several times met with young Rhombogens whose In- 

 fusorigens were such perfect Gastrulae that they were at first mistaken 

 for vermiform stages. Although the fate of the cells of the Infusorigen 

 seemed at tìrst to rob this resemblance of ali significance , I am now 

 disposed to admit not only that there is a possibility, but also even a 

 probability that th e Infusorigen and the vermiform embryo 

 are co- or di nate forra s. That this idea is not wholly faneiful be- 

 coraes at once evident by comparing the Gastrulae seen in figs. 73. 74, 

 76 with the young Infusorigeus in figs. 109 and 1 JO. If any doubt arise 

 as to whether my figures exaggerate the resemblance , it will probably 

 disappear on Consulting Van Beneden's figures 15, 20—24, PI. 1, and 

 47 a, 48 b — 56, PI. 3. Fig. 109 represents a Gastrula in form and 

 structure quite as perfectly as Fig. 73. It is an epibolic Gastrula in both 

 cases , consisting of a large centrai celi partially enveloped by a single 

 layer of smaller cells. Comparing the later stages, figs. 76 and HO, 

 we see that cell-multiplication begins somewhat earlier in the germogen 

 than in the axial cell : but all the essential Gastrula features are stili 

 preserved, and the germogen presents most striking analogies with the 

 axial cell seen in the closed Gastrula of fig. 79. 



I bave never seen the nucleus [n") of the germogen in process of 

 division , and Van Beneden thinks that it never intervenes in the pro- 

 duction of germ-cells. Before we can safely declare that it has nothing 

 whatever to do with this production , we must be able to assign some- 

 thing better than a rairaculous origin to the germ-cells. To assert that 



Mittheilungen a. d. Zoolog. Station zu Neapel. Bd. IV. 4 



