Mr. H. J. Carter on the Spermatohgy of a new species of Nais. 27 



With reference to the formation of the bile, it has ah-eady 

 been observed, that the vesicles of the floating-cells may form a 

 new generation ; and it will also be seen hereafter that they, 

 under other circumstances, may produce spermatozoa. Hence 

 it might be inferred, that where neither of these developments 

 take place, the endoplasm or vital part, which must be present 

 with the oil, perishes ; and that the former being thus lost, their 

 oleaginous contents become subject to the laws of inanimate 

 matter, and so more or less flow together, to form the large 

 amber-coloured bile-globules which appear scattered over the 

 intestine. 



Segmental Organ. 



This (fig. 2 g and fig. 3 ix) is the name proposed by Dr. T. 

 Williams* for a tubular organ that exists in almost all the seg- 

 ments, with the exception of those containing the generative 

 organs, which, as this gentleman has also intimated f, are but 

 mere modifications of it. In some species it is single, in others 

 double (fig. 48 li), as will be seen by looking at the figures of 

 the two Naides now under consideration. 



In Nais fusca the segmental organ is single. It is absent in 

 the segments before the reproductive band ; attains its maximum 

 size in those immediately behind it ; and diminishes gradually 

 towards the tail, where it almost becomes obsolete. Where best 

 developed, it consists of an elliptical body and tubular portion. 

 The former (fig. op), which chiefly owes its size to a more con- 

 voluted state of the latter at this part, is situated on the right 

 side of the body close to the anterior partition or dissepiment, 

 through which its tubular portion is prolonged for a short di- 

 stance, and then terminates in an expanded, slightly constricted, 

 and marginated mouth {o), furnished with long cilia. From 

 this the tube passes back through the elliptical body, in which 

 it becomes exceedingly tortuous, and after issuing from its pos- 

 terior extremity, makes two sinuous revolutions round the seg- 

 ment, and then also ends on the right side {q), midway between 

 the partitions of the segment, where it opens externally and 

 ventro-laterally. Throughout, this tubular organ floats freely in 

 the peritoneal cavity, except where it is fixed by passing through 

 the partition, and where it opens externally ; and throughout, 

 also, it is imbedded in a fine granular substance disposed in lobes 

 around it (into which, on one occasion, I thouglit I could perceive 

 tiie branching-out of a vessel from the tube). The eiha round 

 the internal opening are much larger than those which line the 

 tube, and the movqment of the former sluggish compared with 

 that of the latter, which is very rapid ; neither is there any par- 



* Ann. and Mag. Nat. Hist. vol. xix. j). 393, 185/. t Idem. 



