136 Dr. 0. Zacharias on tlie Reproduction and 



the ovaries of Bracliionus, Noteiis, and Euchlanis, from which 

 that naturalist thinks he may draw the conclusion that in the 

 ovaries of the Rotatoria in question we have an approximation 

 to those forms of ovaries in which (as in Hexapoda and Asel- 

 lina) the production of the germinal vesicles and of the yelk- 

 mass devolves upon different parts of the ovary*. 



According to what I have quite definitely observed in my 

 Rotifer I cannot adopt this view. It certainly appears as if 

 a separate vitelligenous focus existed in such ovaries ; but we 

 soon see the germinal vesicle come into sight in the midst of 

 the swelling and take its place outside the ovary. The swel- 

 ling, which is originally sessile upon the ovary, increases 

 gradually in size and becomes more and more sharply con- 

 stricted off from its place of origin. Finally the conditions 

 are reversed : the maturing ovum gradually attains its defini- 

 tive size, and then we see the much-diminished ovary attached 

 to the ovum, while previously the reverse was the case. 



The separation by constriction is at last completed (in about 

 three or four hours), and the ovum, in which the germinal 

 vesicle with the germinal spot is distinctly visible, drops into 

 the body-cavity, where it is driven to and fro in the most 

 unceremonious manner by the contractions of the animal. 

 The process of separation is so effected that a portion of the 

 enveloping membrane of the ovary is separated with it and 

 transferred to the ovum, so that the embryo in its develop- 

 ment lies in a completely closed hyaline vesicle, which, from 

 its origin and function, is to be regarded as a real uterus 

 (" poche de maturation" Joliet). Under a magnifying-power 

 of 700 diameters, with good definition, the envelope surround- 

 ing the embryo (the presence of which has often been dis- 

 puted) may be recognized with the greatest distinctness. 



The segmentation of the egg of Rotifer is very difficult of 

 observation, because the animals suitable for investigation 

 cannot at pleasure be brought to repose and prevented from 

 creeping about. The application of a compressorium is inju- 

 dicious, as the least pressure exerted upon the objects under 

 observation causes their contraction. There is nothing for it 

 therefore but to arm one's self with patience and to take care 

 to keep the egg constantly in the field of vision by suitable 

 movements of the object-slide. Very often, however, the 

 desirable circumstance occurs that the animalcules attach 

 themselves with the foot, unfold the rotatory organ, and re- 

 main for "ten or twenty minutes in this condition. This 

 happens, however, only when they feel quite comfortable, and 

 the illumination is not too bright. 



* Zeitschr. f. wiss. Zool. vi. (1855), pp. 37, 47, and 94. 



