16 
THE VOYAGE OF H.M.S. CHALLENGER. 
vesicula seminalis is no doubt only a dilatation of the vas deferens at the place where it 
corresponds with the testis. The vesicula seminalis in all the larger specimens was filled 
with a dense mass of very small spermatozoids ; they have the shape of threads, each 
having a length of about 0‘02 mm., and each furnished at the extremity with a very 
small vesicle (PI. I. fig. 6). Between the spermatozoids in the vesicula seminalis small 
empty vesicles are seen, as also others which quite resemble the very small cells of the 
contents of the testis, probably each one of them contains a spermatozoid. 
The length of the canal acting as a vas deferens is not very considerable ; it passes • 
freely through the connective tissue for about 0'25 mm. and then enters into that part 
of the body which represents the thorax of the Cirriped. Figs. 10 and 11 on PL III. show 
sections of the duct before it reaches the thorax, but in the figs. 5 to 8 of PI. III. the 
same canal is represented in the middle of each transverse section of the thorax. In 
fig. 9 the form of the section of the thorax is nearly quadrangular ; this is its shape near 
the place where the vas deferens enters it ; in the sections, however, which more approach 
the other extremity of the canal the thorax is exactly cylindrical, and then its wall is 
parallel to the wall of the genital canal. The diameter of the thorax itself is about 
0'08 mm.; the canal which runs through it longitudinally has a width of CLOS mm. 
Whether it be preferable to designate the cylindrical terminal portion of the thorax as 
“ penis” is, I think, difficult to say ; morphologically it is hardly to be distinguished from 
the appendix of that name in the hermaphrodite Cirriped, which is called by some authors 
a penis, by others an abdomen. 
The nuclei of the cells which surround this canal (PI. I. fig. 5) are slightly larger 
than those of the connective tissue placed between the canal and the chitinous wall of 
the thorax ; as far as I could distinguish in any of the sections, these cejls of the wall of 
the canal have no distinct shape and do not compose a true epithelium. From the place 
where it enters into the thoracic part of the body the vas deferens is seen in all the 
sections which pass transversely through the thorax ; it may be traced for about half a 
millimetre ; it then ends abruptly ; probably, though this could not be distinctly 
observed, it now opens into the cavity (PI. III. fig. 4 ca ) lined by the connective tissue, 
which has an outward opening at the capitular pole of the body. The communication 
with this cavity must be about at the height of the supraoesophageal ganglion. The 
whole thoracic part of the body can be stretched forward in a direction towards the 
capitular pole ; though I do not believe that the opening of the vas deferens ever reaches 
the opening at the surface of the body, this stretching forward of the thorax is no doubt 
brought about in order to approach the opening of the vas deferens as much as possible 
to the slit at the extremity of the body. Well-developed musculi retractores serve for the 
retraction of the thorax within the body of the male. I have figured one of them on 
PI. I. fig. 1, mr. In the transverse section figured on PI. III. fig. 10 these muscles are 
also represented. 
