DESCRIPTIONS OF GENERA AND SPECIES 235 



In Hemitubifex and Psammoryctes the upper end of the spermiducal gland, which 

 is wider in most Tubificidae than the distal region, is more markedly dilated, and 

 is constricted oft' from the rest to form a spherical chamber, receiving the vas deferens 

 and prostate. This has been called the ' vesicula seminalia.' 



Bothrioneuron (fig. 40) has a peculiar efferent apparatus. The terminal chamber 

 is wide, and is continuous above with the spermiducal gland, which is enveloped in a 

 glandular sheath; about halfway down the prostate opens; this prostate (puratrium 

 VEJDOVSKY calls it) is rather different in structure from the prostate of other Tubificidae. 

 It consists of two parts: (i) of a pear-shaped diverticulum of the terminal chamber, 

 lined with tall cells ; (2) of a group of thicker cells, attached to the blind extremity 

 of this. The two efferent ducts open (in B. vejdovskyanum) by a common median 

 pore, a common enough arrangement in the family Eudrilidae, but rare in the aquatic 

 families. Shortly before this common opening are (in B. vejdovskyanwni) two diverticula, 

 one containing penial setae. Bands of muscles are attached to the terminal part of 

 the chamber, which is possibly protrusible. There is no penis as in the genera 

 Tubifex, Spirosperma, &c. 



The terminal efferent apparatus of Tubifex is like that of Limnodrilus ; but the 

 penis has a more complicated structure which has been especially studied by NASSE, 

 DIEFFENBACH, and VEJDOVSKY (24). The latter has described its development, which 

 is as follows. The first appearance of the spermiducal gland is a spherical invagi- 

 nation of the integument into which opens the vas deferens. This sac then lengthens, 

 and the prostate arises from a thickening of the ciliated lining epithelium. The 

 portion of the terminal chamber which lies nearest to the skin then becomes 

 constricted off, and its epithelium breaks up ' into numerous elliptical and bright 

 elements, which completely fill the cavity of the sac, so that only a with difficulty 

 visible canal remains to put the newly formed chamber into communication with 

 the exterior." The further development of these bodies was not traced ; but the 

 penis and its sheath is probably a product of this distal part of the terminal 

 chamber. In the adult worm the penis has a very complicated structure. As in 

 Limnodrilus the canal of the penis is a direct continuation of the atrial canal, 

 and there is a penis- sheath lined with epithelium and covered with muscles 

 externally; this seems to have undergone a second folding, so that the retracted 

 penis is enclosed by two sheaths ; the inner of these secretes a thick, elastic, and, 

 apparently, chitinous membrane, which is inserted on to the penis where the 

 epithelium the matrix of the chitinous membrane becomes continuous with the 

 epithelium of the penis itself. In Tubifex and in Spirosperma also the actual 

 extremity of the penis is formed by a very thick mass of cells surrounding the 



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