Mr. Hi J. Carter on the Spermatology of a new species of Nais. 21 



new species of Nais, together with other matter bearing on the 

 origin of the sperm-cells both of the so-called testes and ovisac ; 

 also on the functions of the floating-cells of the peritoneal cavity, 

 and that contractile body called by Dr. T. Williams the " seg- 

 mental organ*;" — to which is appended a short summary of the 

 changes which successively take place in the yelk during the 

 development of the embryo, and the product which frequently 

 results when the yelk fails to fissurate. 



This information has been chiefly obtained from a perennial 

 species of Nais that, for a year past, has colonized the sediment 

 of a glass jar, in which Char a has been growing out of a little 

 saucer suspended a short distance from the bottom; but not 

 having afforded me any opportunity of following the develop- 

 ment of the embryo, I have been obliged to take advantage of 

 another species for this purpose, which I found in a gelatinous 

 Alga (Gloeocapsa), collected during "the rains," for the micro- 

 scopic Filarice that it also contains, and which species not only 

 furnished me with eggs, but with other observations of a serial 

 nature, that serve to complete those unsupplied by the first 

 species. 



Thus the facts contained in the following pages having been 

 the result of investigations carried on under an unusual com- 

 bination of favourable circumstances, attended with a micro- 

 scopical examination of upwards of two hundred individuals, it 

 is hoped that they will be found acceptable. 



The text, however, is not the consequence of this labour more 

 than the illustrations, which are as true to nature as circum- 

 stances would permit, and have been compiled from a great 

 number of sketches taken from the objects themselves. 



With these few remarks, let us proceed to the following de- 

 scriptions of the two Naides to which I have alluded, which it 

 is desirable to premise, that the reader may be familiarized with 

 their specific and general characters respectively, before he com- 

 mences the subsequent observations. They are, I believe, new ; 

 and the first that will occupy our attention is that species which 

 has colonized the sediment of the jar of Chara, as it is this from 

 which my information has been chiefly derived. 



Nais fusca, H. J. C. (nov. sp.) PL II. figs. 1-3. 



Filiform, of a pinkish-brown colour, subsegmented, setaceous; 

 anterior extremity clavate pointed, posterior extremity slightly 

 attenuated, obtuse ; mouth inferior, a little distance from the 

 anterior extremity; anus subterminal. Reproductive band 

 near the head, commencing with the fifth segment. Cirri 



* Aqii. and Mag. Nat. Hist. vol. xix. p. 393, 1857. 



