3.2 Mr. H.J. Carter on the Sjjei'matology of a new species of Nais. 



and very rapid, as in the tube of the segmental organ, while 

 that of the long cilia round the mouth is comparatively slow, 

 and indicates no more current among the floating-cells and other 

 particles of the peritoneal cavity in juxtaposition, than those on 

 the corresponding part also of the segmental organ. Nor have 

 I ever seen any of the floating-cells in the fallopian tube, though 

 frequently in the oviduct (fig. 3/). It is this instance of the 

 floating-cells passing into the oviduct witJb, instead of against, 

 the movement of the cilia, to which I alluded when speculating 

 upon the functions of the segmental organ. 



The ovisacs (fig. 2 d and 3 h, h) are also extremely delicate, 

 transparent, contractile bags, which, commencing by a narrow 

 neck from the posterior end of each oviduct, extend backwards 

 to the second and third segment behind the reproductive band, 

 where they terminate in round extremities ; beyond this there is 

 nothing remaikable in them when empty, except that they are 

 enveloped and partly supported, as they float in the peritoneal 

 cavity, by long loops of the vessels termed " the branchial sy- 

 stem" by Dr. Williams in Nais filiformis^, but which here are 

 evidently of great service in affording nourishment to the ovum 

 and the spcrin-cells when they are undergoing development in 

 the ovisac. 



Ovary. 



We must assume here, as in many similar cases that how- 

 ever thin and attenuated the ovisac may be, the inner sur- 

 face of its posterior extremity can furnish a point or particle 

 w hich may become an ovicell ; and, for reasons which will be 

 better understood by-and-by, that the ovicell which it can thus 

 j)roduce is composed of a cell-wall lined by a layer of endo- 

 plasm, in the periphery of which is the nucleus, consisting of a 

 nuclear cell and nucleolus ; that the nuclear cell is filled with 

 endoplasm charged with several points or nuclei, which become 

 sun'ounded by, or develope around themselves, as many cells ; 

 and that finally the nucleolus perishes, and leaves these cells 

 alone, or rather enclosed in a delicate membranous envelope 

 (the nuclear cell expanded?). Thus we obtain a group of ova, 

 (fig. 9 c) which, whether developed in the way mentioned or not, 

 make their apjicarance under this form, free and detached from 

 the surface of the ovisac. In general there is only one of these 

 groups present ; but there may be two (fig. 9 c), or even three. 

 Each ovum of the grouj) is, as usual, composed of a cell-wall 

 lined or filled with endo])la.sm, and bearing in one part the 

 nucleus or "germinal vesicle," which consists of a diaphanous 

 cell whose cavity forms the " transparent area," in which again 



* Report of the British Association for 1851, p. 183. 



