208 WAGENERj ON GYRODACTYLUS ELEGANS. 



as well as the vitellus, is slightly opalescent. In the nucleolus 

 may occasionally be seen a second globular body, as clear and 

 well defined as the nucleus itself, the nature of which is un- 

 known. In the oviduct may occasionally be perceived very 

 minute ova (particularly in small Gyrodactyli) , of hardly 

 one third the usual size. It is possible that these may grow 

 while still in the oviduct, which never contains more than 

 one (full sized) ovum. 



Whilst the ovum is lying in the oviduct changes go on in 

 it, which have usually been referred to the influence of im- 

 pregnation. The nucleolus, at first sharply defined, loses its 

 definite outline, and the spot sometimes noticed in it is no 

 longer visible. As the dissolution of the germinal spot proceeds, 

 the nucleus becomes more and more transparent, the space 

 which it occupies being increased in like proportion. At 

 length the perfectly clear nucleus of the ovum is rendered 

 turbid, from the remains of the germinal spot floating about 

 within it. 



I happened, on one occasion, to observe an ovum in this 

 stage make its entrance into the uterus.^ 



The appearances presented in this transit may best be 

 compared with the passage of a viscous substance through a 

 narrow orifice. The drops of vitellus gradually increasing in 

 size, which was protruded from the papilla into the uterine 

 cavity, appeared every moment as if it would be torn off". 

 The nucleus or germinal vesicle was forced towards the 

 entrance of the uterine papilla by the contractions of the 

 animal, which are, apparently, the eff'ective agents in the 

 process. The lower part of its periphery during this, was 

 still surrounded with a pretty thick layer of vitellus. The 

 nucleus or germinal vesicle thus compressed assumed every 

 possible shape, every inequality in the pressure causing a 

 change of form. It appeared to oppose great difficulties 

 to the passage of the ovum. Suddenly it burst, and the 

 ovum rushed into the uterus. 



When the entrance was thus eff'ected tliere was seen, not 

 as might have been supposed from the violence of the pro- 

 ceeding, several drops of matter, or an irregular amorphous 

 mass, but the uterus was occupied by a large, dark, opalescent 

 globular body, whose perfectly uniform aspect resembled 

 very closely the rather lighter yelk of the uninjured ovum. 

 In the case in which the above observation was made the 

 animal perished before segmentation commenced. 



Thus it appeared as if the altered contents of the germinal 

 vesicle became intimately mingled with the vitellus, or that 

 the same process takes place with the germinal vesicle and 



