24 Mr. H. J. Carter on the Spermatology of a new species of Nais. 



lined by a group of vesicles filled with refractive matter, resting 

 on a central sphere equally refractive. There is also a nucleus 

 present (fig. 5 d), which in all probability is held in position by 

 a thin layer of endoplasm situated between the vesicles and the 

 central sphere, and from which vital agent or primordial film all 

 the rest of the cell has been produced. For the most part these 

 cells are diffluent in form (5 a, b), but there are many which 

 are spherical (fig. 7), and the latter average 2- to 3-5600ths of 

 an inch in diameter. The refractive matter with which the 

 vesicles are filled, as well as that which composes the central 

 sphere, appears to be albuminous at first ; but while that of the 

 former, in the vesicles of the floating-cells of the peritoneal 

 cavity, which will presently be seen to be identical to all appear- 

 ance with the cells of the reproductive band, may pass into oil 

 or spermatozoa, that of the latter disappears without further 

 change, or becomes granular in a way which will be better un- 

 derstood hereafter. Certain it is, that the centre of these cells 

 is composed of a solid sphere of refractive substance, which 

 possesses sufficient tenacity to retain its form against the solvent 

 action of water, even after being deprived of the cell- wall 

 (fig. 5 d), and which sphere, we shall find by-and-by, in the 

 floating-cells, affords nourishment to the spermatozoa during 

 their development from these cells in the ovisac. We may safely 

 infer, then, I think, that it contains the elements of both albu- 

 men and oil, which substances are developed in it at the expense 

 of each other, according to the requirements of the case. Dr. 

 Williams considers the albuminous centre of the floating-cells 

 to be a fibrinous compound*. Thus, then, to recapitulate, we 

 have the cells of the reproductive band composed of a cell-wall, 

 a nucleus, and a number of vesicles surrounding an albuminous 

 sphere, which thus occupies the centre of the cell. 



Of the inner sheath or layer (fig. 3 s) nothing need be stated 

 further than that it forms the chief skeleton-support of the body 

 of the Nais, and may be muscular or fibrous, or both. It be- 

 comes separated from the cellular layer under the influence of a 

 solution of bichloride of mercury, and thus may easily be de- 

 monstrated. Between it and the alimentary canal is the peri- 

 toneal cavity, in the " chylaqueous fluid M of which float the 

 floating-cells, segmental organ, organs of generation, and a good 

 part of the vascular system. 



Alimentary Canal. 



This (fig. 2 a, /, /) forms, as above stated, a third or central 

 cylinder, suspended inside the second by the delicate loose por- 



* Phil. Trans, part 2. p. 625 el seq., 1852. 



