178 BALBIANIj ON SEXUAL 



nating; they copulate, though destitute of copulatory 

 organs. The " nucleus'^ of these animals is, in truth, an 

 ovary ; the " nucleolus^^ a testis. Each of these parts may 

 have its special excretory duct, opening on the outer surface 

 of the body. Thus the whole reproductive apparatus forms 

 a system distinct in itself, and there is no internal generative 

 cavity. 



The Nucleus or Ovary, 



The ovary varies much in form and size, less so in posi- 

 tion. Always somewhat excentric, it appears, in many cases, 

 attached to the cortical layer, from which it freely projects 

 into the mass of soft tissue, forming the inner suljstance of 

 the Infusorium. This attachment may be of such a nature 

 as to allow the ovary very little power of shifting itself about 

 within the interior of the animal. Or it may engage so 

 trifling an extent of surface that the female organ seems to 

 undergo considerable changes of place, sometimes making its 

 appearance about the middle of the body, sometimes towards 

 one of its extremities. 



Von Siebold, in describing the nucleus, states that "'it 

 appears to lie very loosely in the parenchyma, and some- 

 times individuals may be observed turning their bodies 

 around it as it rests motionless in the centre. ^^ But M. 

 Balbiani shows that this immovability of the nucleus is only 

 apparent, not real. For in certain Infusoria the body is 

 remarkably depressed, and the ovary so large, as almost to 

 be in contact with its opposite sides. To convince ourselves 

 that this organ takes part in the general rotation, we have 

 only, he says, to examine some large Infusorium when much 

 dilated with water and other ingesta. " As the animal turns 

 round on itself we clearly perceive the nucleus describe a 

 circle about the axis of revolution, and by turns approach and 

 withdraw itself from the focal plane of the microscope.'^ 



Histologically, the ovary consists of a number of very fine 

 granular particles, held together by a pretty compact gelati- 

 nous tissue, the whole being enclosed in an outer membrane 

 of extreme tenuity, and destitute of any apparent structure. 

 So transparent is this envelope that, when examined in situ, 

 it is at first impossible to distinguish it from the granular 

 mass which it invests. A drop of dilute acid, however, soon 

 causes this mass to contract, and the delicate ovarian wall, 

 thus separated from its contents, becomes clearly visible. The 

 same result may be obtained, though more slowly, by the 

 endosmotic action of water on the ovary pre\iously removed 



