Mr. ?I. J. Carter on the Spermatulogy of a new species o/Nais. 31 



composed, being to all appearance, as before stated, identical 

 with the floating-cells (from which we shall by-and-by find the 

 spermatozoa to be developed in the ovisac), have some means 

 perha])s of getting into the testes by a channel as yet undis- 

 covered, and there becoming subservient to the same purposes ; 

 for, as I have already observed, there are cells in the testes 

 sometimes which bear all the characters of the spermatic cells of 

 the ovisac. 



Thus the so-called testis appears to be a sac for holding the 

 sperm-cells during the development of the spermatozoa, rather 

 than for providing these cells; while, should the latter be de- 

 rived from the reproductive band, this baud would be more 

 appropriately termed the testis. 



Although, however, I have not been able to trace the develop- 

 ment of the spermatozoa in the testes of Nais fusca, yet I have 

 been able to do so in N. albida (PI. IV. figs. 31-33) ; but as the 

 process is the same as that which I shall have presently to detail 

 in the ovisac, it is better not to go further here than barely to 

 mention this fact. 



Oviducts; Fallopian Tubes; Ovisacs. 



The oviducts (fig. 2 c and 3 /) are elliptical, transparent, deli- 

 cate sacs situated under the reproductive band, on each side of 

 the median line ; they have wrongly been called " uteri,^^ for they 

 are no more deserving of this name than the oviducts of a fowl. 

 They are endowed with a motile power which manifests itself 

 almost rhythmically, by sudden contraction, so that at first they 

 look like large *' contracting vesicles.'^ Each has three aper- 

 tures, viz. one [g] inferior, which opens ventrally, and may be 

 termed the vaginal aperture ; another, in the anterior extremity, 

 which is continuous with the so-called fallopian tube {c) ; and 

 the third in the posterior extremity, which is continuous w4th 

 the ovisac (k). It is this saccular duct which probably holds the 

 ovum for a short time, during the addition of the horny shell. 



The so-called fallopian tubes (e') are, again, wrongly named, 

 because they do not convey the ova into the ovisac, but, on the 

 contrary, as we shall see presently, convey the floating-cells of 

 the peritoneal cavity into the oviduct, previous to their passing 

 into the ovisac, where they become sperm-cells. They are sim- 

 ple tubular prolongations of the oviduct, which, passing through 

 the partition of the preceding segment, thus become fixed in 

 their position, and open freely into the cavity of the peritoneum 

 close to the testes (e). Each tube is ciliated internally, and ter- 

 minates in an expanded aperture, whose iinier margin is also 

 surrounded by a fringe of long, straight, coarse cilia. The 

 direction of the motion of the cilia in the tube is backwards, 



