MORPHOLOGY OF CYCLOPS. 37 



its epithelium is large, coluninav, 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 (PI. II. fig. 2, i\d.), which 

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

 and runs ol)li(|uely 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 semlnalls (PI. II. figs. 2 & 5, ve.s.) which, 

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



The vas deferens has a \qv\ thin membranous Avail lined by tabular cells ; within this 

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

 packed Avith 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 bodilj^ 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 sul:)stance in which the 

 spermatozoa are apparently imbedded, which 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, Avhich show a refractile streak, 

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

 3. Roimded bodies, Avhich in Avater swell up, shoAving a clear space round a nucleus, 

 distinctly reticulated (after staining AAdth 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 eff'ect, the expul- 

 sion of the spei-matozoa into the spermatheca. What, then, are these bodies? It is 

 evident that they correspond with the large nuclei seen in the vas deferens, and 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, Avhich he justifies by a 

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

 A^iew is my obserA'ation that, on staining after the action of Avater, in both epididymis and 

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

 in the sAvelling of its unstained envelope, Avhich before Avas closely applied to the nucleus. 

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

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

 testis. The intermediate substance, of Avhicli 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 A'as deferens*. 



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



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

 actively undulating in the hody of a male Cijpris, half crushed by the cover. 



