184 MR W. E. HOYLE ON 



but there is no intimate union between the two, which are separated by a clear 

 line of demarcation. 



The truth of this observation, so exactly opposed to what might have been 

 expected, has been confirmed by the preparation of a very careful series of 

 transverse sections, which show the one tube lined with a perfectly smooth 

 layer of epithelium, passing by the other, utterly ignoring, if the expression may 

 be allowed, its proximity, while the vesicula seminalis fades away in a mass of 

 rather loose cells without showing the least desire to unite with its companion. 



PI. XXVIII. fig. 15, shows the last section which contains a trace of the 

 vesicula seminalis, in the one next behind the lumen, though small, was quite 

 apparent, and in the next anterior there is no trace of it whatsoever. 



Observations suggested by this arrangement will be deferred until the next 

 portion of the generative system has been described. 



3. The Vas deferens (Pl.-XXVIII. figs. 1, 10, and 12, v.d) is a short tube which 

 passes' forwards from the termination of the vesicula seminalis and opens into 

 the cirrus sac ; this portion of it is about 15 to 2 mm. in length, but it is pro- 

 longed backwards into accecal process (blindschlauchartiger Anhang, Leuckart) 

 whose length commonly exceeds that of the anterior portion by two to three 

 times ; it is variously curved, and in caie case was observed to open again into 

 itself, and thus to form a complete tubular ring. 



The structure of this vessel is the same throughout, its average diameter is 

 about 6"08 mm., that of its lumen 0*024 mm.; within it is lined by a thin layer 

 of chitin derived from the external covering of the body, externally to which is 

 seen a compact mass of nucleated cells radially disposed and to all appearance 

 epithelial in nature. I was unable to discover with certainty the presence of 

 muscular elements in this wall, although Leuckart observed them in L. tamioides, 

 and based upon that fact the hypothesis that the ccecal prolongation is an organ 

 for the propulsion of the semen. # For the greater part of its length it possesses 

 a further adventitious covering of tissue similar to that in which the vesicula 

 seminalis terminates. 



The opening of this organ into the cirrus sac will be described under that 

 heading (p. 185). 



The want of continuity between the vesicula seminalis and the vas deferens 

 becomes comprehensible wjien we consider what is known of the developmental 

 history of this group of animals, for it would appear from the researches of 

 Leuckart that one portion of the generative apparatus takes origin by the 

 segregation of cells within the body, while another portion is formed by 

 invagination of the external surface. When it is remembered that the vas 

 deferens is connected with the external surface, and bears further marks of its 

 origin in its chitinous lining, and that the vesicula seminalis presents a marked 



* Loc. cit., p. 75. 



