^VAGENER, ON GYKODACTYLUS ELEGATTS^. 211 



also disappear, when the hooklets and hooks of the caudal 

 disc may be viewed even with a low magnifying power, and 

 the egg-shaped mass, now composed of uniform large cells, 

 is seen of considerable size in the interior of the embryo. 



In the further development of the embryo the cells con- 

 stituting the future cephalic portion are the first to be 

 reduced to the smallest size. A furrow which commences as 

 a shallow lateral groove, and gradually increases in depth 

 whilst advancing in an oblique direction from below to above, 

 marks off the cephalic portion. 



A transverse furrow indicates the boundary of the caudal 

 disc ; and fine lines mark the limits of the various organs, 

 amongst Avhich the ovary and the so-termed unicellular 

 glands are distinguished by the size of the cells composing 

 them, whilst the cells which constitute the cephalic extremity 

 of the animal gradually lose their distinctness. 



The mature embryo lies in a curved posture in the uterus, 

 the head and tail being placed together, touching with their 

 neutral surfaces. 



The uterus of the embryo, even at this time, contains a 

 second progeny in the shape of an embryo, whose hooklets are 

 already pedunculate, although it still manifestly consists only 

 of cells. The rudiments of the organs begin to be visible 

 here and there, and the situation of the ovary is indicated 

 bv some cells remarkable for their size. 



In the interior of this second embryo, in the situation where 

 the uterus is placed, even at this time may be seen an oval 

 aggregation of cells, which manifestly presents at its lower 

 end sixteen radiating hooklets ; behind which are visible the 

 two points of the large hooks. 



Within the second embryo also, with some attention will be 

 perceived an elliptical marking, which likewise corresponds to 

 the situation where the future uterus is to appear. At this 

 spot the cells are somewhat larger, but of very unequal size. 



An embryo of this kind, at the period when an ovum is 

 perceptible in the oviduct, spermatozoa in the testes, and in 

 which all the organs are fully formed, is ripe for expulsion. 

 The uterus, whose much distended walls are no longer covered 

 with the granular layer, embraces it closely. The act of 

 parturition is very sudden ; and the embryo escapes on the 

 ventral aspect of the body close to the penis, through an 

 orifice which, as before said, closes immediately. 



The newly born perfectly mature Gyrodactylus resembles 

 its parent in every respect, except that it is a little smaller. 

 In its uterus may be distinctly seen two successive generations 

 lodged one within the other, and easily recognisable by the 



