182 MR VV. E. HOYLE ON 



a few masses of protoplasm of very variable size and shape, each usually 

 possessing several nuclei, but not divided into distinct cells (fig. 2) ; they clearly 

 represent the earlier stages in the development of the spermatozoa as figured by 

 Leuckart."* Anteriorly, as well as posteriorly, the testis becomes narrower 

 though not to the same extent, and its inferior wall becomes thickened by a 

 deposition of small cells on its outer surface. Farther forward two grooves 

 appear in this mass of cells, which gradually become deeper until eventually 

 they become roofed in, and thus converted into two tubes (figs. 4 and 5). 

 The tissue in which these tubes lie is composed of small rounded cells, which 

 vary from 0*004 mm. to O'OOS mm. in diameter, and are provided with small 

 spheroidal nuclei. In the tubes they seem to form a single layer of columnar 

 epithelium, but this was so badly preserved that I can give no further 

 particulars concerning it. 



The lumen of these tubes gradually becomes regularly oval and very much 

 smaller, being in some sections barely perceptible, and in certain cases the cells 

 seem to have a tendency to segregate into a separate covering for each tube, 

 as indicated by a splitting in the cell mass ; these fissures do not, however, 

 extend far, and may be due only to the shrinking of the tissue in hardening 

 (fig. 6). 



On examination of PL XXVIII. figs. 4-6, it will be noticed that the cavity 

 of the testis extends forwards some distance over this tube, but it becomes 

 gradually smaller and eventually terminates blindly. 



These two tubes continue separate although enclosed within a common 

 investment for a distance of 0*2 mm., and then fuse into a thinner walled 

 cavity, roughly oblong in section, and supported by a continuation of the same 

 mesentery as the testis. At this point we may consider the second part of the 

 genital tract to begin. 



The two tubes are, of course, indications of the primitive symmetry of the 

 sexual organs, and it may be worth while to mention that in L. tcenioides the 

 testis is double (though both glands eventually open into an unpaired tube), 

 while in P. oxycephalum and P. proboscideum only a single gland is present. 



2. The Vesicula seminalis (PI. XXVIII. fig. 1, v.s), (Samenblase, Leuckart). 

 I apply this name to the structures now to be described, because they seem 

 to correspond to a tube, bifurcated at its extremity in L. tcenioides, and near 

 its commencement in P. proboscideum. In the present instance the lumina of 

 the two tubes become united, and also first enlarged, for as may be seen by 

 comparing figs. 6 and 7, the cavity of the single vessel is much greater than 

 those of its two components. The wall is made up of cells of precisely the 

 same character, but is only about 024 mm. in thickness on the average. 

 The layer of columnar epithelium is distinct in its interior. 



* Log. eft., Tab. ii. fig. 14. 



