166 ON TUBIFEX RIVULORUM. 



contains both male and female organs. According to Claparede, 

 the male organs consist of the testes and vasa deferentia ; the 

 former number at least two, and sometimes three in mature speci- 

 mens. The first of these is found in the ninth segment (see Fig. 

 I, PI. ;^;^, and the second in the eleventh, whence in course of 

 development it invades the proximate segments, sometimes so far 

 as the fifteenth, by pushing before it, in the form of a sac, the 

 septa which divide one segment from another. A third testis is 

 described as being sometimes found in the eleventh or twelfth 

 segments, and lying in a separate sac alongside the second. 

 These three testes have all a very similar appearance, and enclose 

 spermatozoa in all stages of development. When the spermatozoa 

 arrive at maturity, they escape, by the rupture of their containing 

 sac, into the perivisceral cavity, where they may be found abun- 

 dantly in the tenth and eleventh segments, attached, as he says, to 

 their " spheres of development." 



The vas deferens (Fig. 3) is a modified and extraordinarily 

 developed segmental organ, composed of three parts, which he 

 calls respectively the funnel, the ciliary tube, and the atrium. 

 This latter communicates with the intromittent organ. The 

 funnel is found in the septum separating the tenth from the 

 eleventh segments, its cavity opening into the former, and pre- 

 sents the appearance of a cup, the edge of which is fringed with 

 cilia, in which, at the epoch of maturity, the spermatozoa are 

 entangled. With the funnel is connected a long, convoluted 

 ciliary tube, the coils of which occupy the eleventh and some- 

 times the twelfth segments. It is regularly striated, which appear- 

 ance is due to the presence of a series of fusiform unicellular 

 fibres, disposed circularly round the ducts in such a manner, that 

 the thick part of one lies next to the thin part of the ring which 

 precedes it, thus allowing a succession of these rings to constitute 

 a cylinder (see Fig. 2). The interior of the duct thus formed is 

 ciliated. The atrium is the lower and dilated portion of the vas 

 deferens, and is described by Claparede as having a thick outer 

 wall, inside which is a delicate membranous one, and inside this 

 again is a ciliated epithelium. It communicates with the intro- 

 mittent organ. 



An organ which, for want of a better name, he calls a seminal 



