Mr. A. Hancock on the Anatomy of Oithona. 295 



Reproductive Organs. — There are two external orifices, one 

 placed a little in advance of the other on the right side of the 

 head between and a Httle below the tentacles. The one (PI. IX. 

 fig. 1 a) in front is for the exsertion of tlie intromittent organ, 

 the other [b) is rather small and is common to both the female 

 and androg}Tious apparatus. 



On laying open the dorsal skin, the reproductible organs are 

 found as usual to occupy much of the ^■isceral cavity, ha\-ing the 

 stomach and intestine lying above, and the buccal mass in front. 

 The intromittent organ (PI. X. fig. 2 a) is placed in advance of 

 the other parts, and, in its retracted state, is long, rather slender, 

 and linear ; difiering considerably from the usual conical form of 

 this organ when in this state. The outer extremity leads thi-ough 

 the wall of the visceral ca%4ty to the external orifice, and on its 

 ■way the sheath or external covering becomes firmly attached to 

 the muscles of the skin. The testis (6), a stout flesh-coloured 

 tube two or three times convoluted, tapers at one extremity into 

 a long slender duct or vas deferens (c), which is united to the 

 inner extremity of the penis. The other extremity of the testis 

 suddenly contracts into an equally slender duct (</), but very 

 much shorter, and is joined by this duct to the oviduct. The 

 ovary (e) fills the posterior portion of the visceral cavity, and is 

 composed of large irregular lobules made up almost entirely of 

 eggs, and packed into a dense mass, tapering a little behind and 

 truncated in front. The o\-iduct (/) leaves the anterior border 

 of the ovary as a slender tube, but, almost immediately dilating (y), 

 equals the diameter of the testis. This dilated portion of the 

 oviduct rests between the lobes of the mucus-gland, and is at 

 first somewhat sacculated and convoluted ; it then passes forward 

 and suddenly contracts [h) to its original diameter, and then ad- 

 vances to the anterior border of the mucus-gland and receives 

 the duct from the testis as before described; it then bends a 

 little backward and is shortly joined by a duct {k) from the sper- 

 matheca. This latter organ {j) is a small oval membranous sac, 

 lying between the lobes and at the front margin of the mucus- 

 gland. The duct, which is short and slender, passes from one 

 end of the sac, and, at the point where the duct is united to the 

 o>'iduct, it is joined by a tube [m) which comes from the external 

 orifice immediately within the female opening. This tube is the 

 vagina or copulatory channel, and is cemented to the upper wall 

 of the female channel. Just before the vagina reaches the duct 

 of the spermatheca and oviduct, it gives ofi" a branch which sinks 

 into the female channel, and so far may be looked upon as a 

 portion of the oviduct, for it is by this branch that the eggs find 

 their way to the female outlet. 



The mucus-gland (n, n, w'), for the secretion of the mucus-like 



