H14 



EMBRYOLOGY 



larva and in the Rotatoria. As regards the rest of the organi- 

 zation — for example, the structure of the nervous system — 

 Binopliilns has been compared directly to the Archiannelida. 



Dinophilus lays its eggs, several united, in transparent 

 gelatinous capsules. In Dinophilus apatris (gyrociliatus) 

 there are found in the capsules, in addition to the large oval 

 eggs, spherical ones, which are several times smaller ; the 

 number of the former compared to the latter is about as two 

 to one. From the larger eggs arise the females, from the 

 smaller the males, when, as in D. apatris (gyrociliatus), 

 there is a great difference in the size and form of the two 

 sexes (Korschelt). 



Cleavage is unequal in both kinds of eggs, and, according 

 to Korschelt's statements, which are corroborated by 

 Harm ER, leads to the formation of an epibolic gastrula. 

 Repiachoff, on the contrary, describes the occurrence of an 

 invagination gastrula for the large eggs of D. gyrnciliatus, 

 which arose from a blastula thickened on one side. The 

 blastopore appears to become the mouth. Two large 

 cells are differentiated near it, which, according to Repia- 

 CHOFf's observations, move into the blastocoele, and there, as 

 in other Annelida, produce the two mesodermal bands. The 

 supi-a-oesophageal ganglion is to be seen lying close to the 

 ectoderm. 



However, the accounts last mentioned do not seem to be 

 well established ; but what is known of the development of 

 Dinophilus harmonizes with Annelid development, and the 

 entire organization of the worm points to relationships with 

 the Annelida, 



From the fact that a most striking sexual dimorphism 

 exists in Diimphilus, — in so far as the males are much smaller 

 and more simply organized than the females, lacking the 

 intestine, the eyes, and the segmental bands of cilia (Kor- 

 schelt), — relationships of this genus with the Rotatoria have 

 also been contended for ; but these conclusions do not appear 

 to be justified when one reflects that, while sexual dimor- 

 phism makes its appeai^ance in certain species (D. apatris, 

 i.e., D. gyrociliatus), in very similar species, such as D. vorti- 

 coides, gigas, and tceniatus (according to 0. Schmidt, Weldon, 



