MOKPHOLOGY. OF CYCLOPS. 37 



its ejntheliuiH is large, columnar, vacuolated, and spongy-looking. There is hardly any 

 membranous wall, and where the two limbs are in contact their epithelial cells dovetail 

 in with one another in this as in most species of Cyclops. The second limb a little before 

 its end undergoes the change to the characters of the vas deferens (PL II. fig. 2, v.d.), which 

 after running to the junction of the vas efferens and first limb, bends at an acute angle, 

 and runs obliquely downwards and outwards for a short distance and then backwards, 

 following nearly the same course as the oviduct, but is rather more wavy. It opens on 

 the inner side of the large reniform vesicula seminalis (PL II. figs. 2 & 5, ve.s.) which, 

 with its fellow, fills the ventral enlargement of the sixth thoracic segment. 



The vas deferens has a very tbin membranous wall lined by tabular cells ; within this 

 it contains a structureless membrane, the wall of the spermatophore, forming a tube closely 

 packed with spermatozoa, intermixed with deep-coloured nuclei in stained specimens, and 

 extending back to the end of the third thoracic segment, beyond which it narrows greatly. 

 The substance forming the wall of the spermatophore seems to be extensile ; a segment 

 of it must come down bodily into the vesicula seminalis, whereof it follows the reniform 

 contour of the cavity. 



The vesicula seminalis is reniform, and occupies with its fellow the ventral part of 

 the last thoracic segment. Its wall is thin and chitinized inside. 



The contents of the spermatophore are of three kinds : — 1. A substance in which the 

 spermatozoa are apparently imbedded, wbich swells up in water, becoming at the same 

 time richly vacuolated. 2. The ordinary spermatozoa, rod-like bodies, slightly wavy, not 

 readily stained, but in water swelling up into disks, which show a refractile streak, 

 staining in watery logwood dye (Draper's ink, formerly recommended in the Q. J. M. S.). 

 3. Hounded bodies, which in water swell up, showing a clear space round a nucleus, 

 distinctly reticulated (after staining with logwood). In the mature spermatophore these 

 balls, at first mixed with the spermatozoa, become concentrated (by migration ?) into a 

 layer lining the wall, and by their swelling contribute to, if they do not effect, the expul- 

 sion of the spermatozoa into the spermatheca. What, then, are these bodies? It is 

 evident that they correspond with the large nuclei seen in the vas deferens, aud they 

 must be either elements formed in the epididymis, or, as Gruber (who does not seem to 

 have employed reagents) suggests, a second form of spermatozoa, which he justifies by a 

 comparison with the dimorphic spermatozoa of the Isopoda. A confirmation of this 

 view is my observation that, on staining after the action of water, in both epididymis and 

 vesicula seminalis, we are able to make out a stained nucleus which has taken no share 

 in the swelling of its unstained envelope, which before was closely applied to the nucleus. 

 In this case the cells of the epididymis must supply the nutriment to bring about this 

 enlargement of some of the spermatozoa, as no such differentiation is observable in the 

 testis. The intermediate substance, of which a distinct plug is found at the mouth of 

 the spermatophore, is probably a secretion of the epididymis, for it invests the sperma- 

 tozoa in the vas deferens*. 



I have never been able to observe closely the union of the sexes. From the accounts 



* Movement has been denied to spermatozoa in all Crustacea save Cirripeds. I have seen them distinctly and 

 actively undulating in the body of a male Oypris, half crushed by the cover. 



