Mr. H. J. Carter o« the Sp&'matology of a new sjoecies of Nais. 25 



tions of membrane which compose the dissepiments or partitions 

 of the body, and thus floats freely within this space throughout 

 its whole course, becoming surrounded by the layer of hepatic 

 cells only after it emerges from behind the posterior border of 

 the reproductive band, that is, where the oesophagus ends. 



Flo at in ff Cells^. 



Throughout the peritoneal cavity, that is, from one end of 

 the Nais to the other, are a number of spherical cells (fig. 3 b,b,b, 

 and fig. 7), varying in size from 2- to 3-5600ths of an inch in 

 diameter. Most of these are loose, hence the name of " floating- 

 cells," while many adhere to the parietes of the peritoneal 

 cavity through the plasticity of their cell-wall. In composition 

 they are identical, as just stated, with the cells of the reproduc- 

 tive band; and therefore, to avoid repetition, the reader is re- 

 quested to refer to the latter for this part of their description. 

 How they are produced, I am ignorant ; but they make their 

 appearance in the young Nais before the hepatic cells and before 

 the reproductive band. If they were reproduced by fissiparation, 

 one ought, among such numbers, to be able to see this taking 

 place in all its stages ; but such is not the case : it is true 

 that two, three, or more are often seen adhering together, but 

 this may arise from the plasticity of their coats. As they are 

 seen of all sizes, however, it seems not improbable that their 

 vesicles may sometimes become the young litter, and thus the 

 supply may be kept up ; or, indeed, they may be developed from 

 the surface of the peritoneum, which thus acting as a basement- 

 membrane, may have developed them from the commencement. 

 When these cells are subjected to the influence of a solution of 

 bichloride of mercury within the worm, their vesicles expand, 

 burst, and become un distinguishable from the albuminous centre, 

 while the nucleus, remaining, thus becomes distinctly visible 

 (fig. 7 c) : when also they issue into pure water, from a rupture 

 of the body, the same changes take place ; but when the internal 

 vesicles have been formed for some time, or present a yellowish 

 tinge, they remain unaltered; in which case the delicate cell- 

 wall frequently disappears and leaves them adhering to the re- 

 fractive albuminous sphere, which is just as tenacious as that of 

 the cells of the n^productive band (fig. 7 h). Indeed, the com- 

 position of the whole cell, as before stated, is exactly the same. 



Hepatic Cells. 



These are spherical or diflluent in form (fig. 8), and composed 



* For an account of these cells generally in the Invertebrate animals, 

 iiiul tlic •' (Jliylafjuoous Fluid" above mentioned, see Dr. T. Williams's 

 excellent paper, Phil. Trans. \'6b2, p. 5^5. pt. 2. 



