ON GYRODACTYLUS ELEGANS. 161 
Nerves have not as yet been discovered, and this species is remark- 
able for the absence of the four so-called eye spots which have 
been observed in every other species of the genus. The ovary is 
a large organ of somewhat crescentic form, occupying the posterior 
third of the length of the animal, Fig. 430 v. Its blind end appears 
to be occupied by a mass of protoplasm, containing nuclei, but not 
divided into distinct cells. As the oviduct is approached distinct 
cells are found, consisting of a conspicuous nucleus, contain- 
ing a nucleolus, and surrounded by a layer of protoplasm. 
These are the young ova. A mature ovum, such as may frequently 
be seen in the oviduct, Fig. 43 ov m, and Fig. 48, is generally more 
or less oval in form, and consists of finely granular protoplasm, 
-\\ gs 
egy) nh gu 
XS | Yi 
Fig. 48. 
containing a large, clear nucleus, now called the germinal vesicle, 
and a darker granular nucleolus, the germinal spot. 
In many Trematodes an accessory organ, known as the yolk 
gland, assists in the formation of the ovum, and I am inclined to 
think that such an organ exists in a rudimentary form in Gyro- 
dactylus, but I am not yet in a position to speak positively on 
this point. 
The oviduct is a short, wide tube, Fig. 43 0 vd, opening into the 
uterus upon the posterior border of that organ. It is bounded 
laterally by the branches of the intestine, and is partially overlapped 
by the testis. 
The uterus, Fig. 43 «7s, is rounded in form, and occupies nearly 
the whole of the middle third of the body. In the absence of an 
embryo, its cavity is filled with a clear fluid, and its membranous 
wall, «7s, is lined by a thick granular layer, wg /, which at the 
point of entrance of the oviduct forms a perforated papilla, Z /, 
through which the ova escape into the uterine cavity. 
The testis is a conical or heart-shaped body, Fig 43 ¢s, its base 
being applied to the upper wall of the oviduct. Its lateral borders, 
like the oviduct, are bounded by the branches of the intestine. 
According to Wagener, the vas deferens opens upon the upper wall 
of the oviduct. The spermatozoa are simple filaments. During 
the past four months I have had Gyrodactylus under observation 
almost daily, and have only seen two spermatozoa. One appeared 
