184 UALUIANl, OX SEXUAL 



each into two similar parts^ and " in the ovary these parts 

 are situate one behind the other, under the form of little 

 elongated masses following the axis of the body, and sepa- 

 rated by an interval occupied solely by the membraneous wall, 

 equal to once or twice the length of each segment." Hence 

 some observers have not hesitated to ascribe a pair of indepen- 

 dent nuclei to these animals. Yet, INI. Balbiani is convinced 

 that, in spite of this apparantly complete division of its con- 

 tents, the delicate ovarian wall still remains entire, being 

 alike continuous over the separated yolk-masses and the 

 interval which lies between them. Great practical difficulties, 

 however, attend the actual demonstration of its presence in 

 this intermediate region. " But with the aid of high magni- 

 fying powers and the use of suitable reagents, such as tincture 

 of iodine diluted with water, I have more than once succeeded 

 in perceiving it under the form of a clear band, bordered on 

 each side by a very dai"k line, running from one nucleus to 

 the other. Under these circumstance, the two bodies may 

 sometimes be seen to approach one another by a quick 

 simultaneous movement, as soon as the action of the reagent 

 has commenced. This eflFect, Avhicli obviously can only be 

 due to the sudden contraction of a membrane connecting the 

 two nuclei, affords a physiological proof of its existence 

 not less convincing." Frequently, also, the addition of 

 an ammoniacal solution of carmine demonstrates the exist- 

 ence, within this connecting membrane, of a delicate com- 

 missural thread, radiating between the two yolk-masses, and 

 composed of the transparent tissue which binds together their 

 numerous fine granules. 



Some Oxytrichina occasionally exhibit an abnormal trans- 

 verse segmentation of each of the two ovarian elements, 

 similar to that already noticed in the case of Paramecium 

 bursaria ; four nuclear masses being thus produced. 



" But this quadripartite division of the intra-ovarian sub- 

 stance, which appears as a pure accident in the great majority 

 of Oxytrichina, becomes a permanent and normal condition 

 in other members of the group." Thus, in Onychodromus 

 grandis of Stein, the ovary consists of four equivalent 

 portions, arranged in longitudinal series, one behind the 

 other. 



In other cases a still further multiplication of 'the yolk- 

 masses occurs. So numerous do its fragments become in 

 Urostyla grandis of Ehrenberg that, at the first glance, this 

 species might be looked upon as having no nucleus at all, its 

 numerous divisions being scarcely distinguishable amid the 

 small pieces of food and other miscellaneous particles lying in 



