narrowed part only becomes visible at times, when filled with 

 faeces. — The heart is easily observable in the living animal, 

 on account of its very rapid pulsations. It has the form of a 

 rather small hyaline vesicle, located immediately beneath the 

 dorsal skin at the junction between the 3rd and 4th segment. 

 — The ovaries are at times very conspicuous, extending as they 

 do through most part of the anterior division of the body. 

 They constitute two rather large tubes, filled up by a dark 

 green content, and being somewhat irregular flexuose, the ante- 

 rior part lying in a higher level than the rest and close to- 

 gether, whereas the remaining part extends on either side 

 nearer the ventral face, forming in each segment a slight 

 lateral dilatation. The content of these tubes is on closer exa- 

 mination found to consist of rather large ova filled by an opaque 

 granular yolk and generally arranged in a single series, whereas 

 developing egg-cells do not occur. The true germinative layer 

 is much more difficult to examine, on account of its great pel- 

 lucidity. This part forms a single median body lying near the 

 dorsal face, immediately in front of the heart, and best observed 

 in a lateral aspect of the animal (fig. 13). It is found to be 

 built up of numerous clair cellules of different size, all provided 

 with a very conspicuous nucleus, in the inner of which a more 

 opaque body, the nucleolus, is generally traced. The ova, after 

 having attained maturity, are successively forced through the 

 oviducts, which open on the ventral side of the first caudal 

 segment at the tip of the rounded protuberance occurring there. 

 By some secret the ova poured out from the body are held 

 together and enclosed within a pellucid envelop, forming a 

 large flattened sac adhering to the base of the tail (see figs l3 ' 

 13). They are arranged here with rather great regularity an 

 generally pass their development in a very short time, the yoflBg 

 escaping as small nauplii of the well-known imperfect ap- 

 pearance. 



Description of the male. — The adult male (PL VIII, & ^ 

 exhibits an aspect very unlike that of the female. It is als0 * 

 somewhat smaller size, very little exceeding l 1 /* mm. in lengt ' 



