286 THOS. H. MONTGOMERY, 



Like the testis, the wall of the vesicle (Fig. 243, Plate 24) con- 

 sists of a layer of nurse cells (Yk. C) on the surface of a layer of 

 intersecting muscle fibres {M. C). But the inner boundary of this wall 

 is formed by an epithelium of large cells, apparently of glandular 

 function judging by the vacuolated nature of their cytoplasm, and 

 which probably produce the thin find filling the vesicle {Gl. C. V). At 

 the proximal end of the vesicle these cells come into contact with the 

 slender gland cells of the distal portion of the testis (Fig. 251); but 

 these two kinds of gland cells do not seem to pass gradually into 

 one another, though they possibly do so at an early ontogenetic stage. 

 The cell boundaries of the much more flattened gland cells (Fig. 243) 

 of the vesicle can be seen clearly only on paratangential section ; their 

 nuclei are huge, irregular in form and often with the nuclear membrane 

 thickened at some points, thin at others (which demonstrates an active 

 metabolic activity), and contain large true nucleoli of varying form 

 and number. 



In one single testis, and one only, and abnormal vesicle was 

 present (F Fig. 247). This testis was attached at its distal end to 

 a perfectly normal vesicle, but anterior to this there was a second 

 vesicle (F) of elongate form as a bulging-out of the wall of the 

 testis (jT). The elongate axis of this vesicle was at right angles to 

 that of the testis; and in this vesicle were spermatids and spermato- 

 zoa as in a normal vesicle. In all probability this vesicle should 

 be regarded as having arisen as simple hernia of the testis, into 

 which germ cells had lodged and there developed into sper- 

 matozoa. 



3. The Vas Deferens. 



The proximal end of the vas, where it joins the vesicle (Fig. 252), 

 is constricted, and its inner boundary is formed by slender gland 

 cells like those of the distal end of the testis ; unhke that portion of 

 the testis, this narrow glandular portion extends for a longer distance ; 

 in its wall the muscular layer is likewise thickened. On this con- 

 stricted portion follows the wider portion of the vas, the wall of which 

 (Fig. 249) has the same structure as that of the vesicle, namely an 

 outer layer of nurse cells (like those of the testis), an intermediate 

 layer of interlacing muscle fibres {M. C), and an inner epithelium of 

 large flattened gland cells {Gl. C). On account of the similarity in 

 structure of the wall of the vesicle and vas, we may conclude that 

 the former has arisen as a differentiation of the latter. 



