REPKODUCTION IN THE INFUSORIA. 181 



fore, is Decessaiy, in order not to confonnd the nucleolus with 

 the fat globules scattered around it. But the little circle 

 which surrounds it under the circumstances mentioned above, 

 its constant presence, and the — in all cases — identical condi- 

 tions, both as to number and position, which it offers in a 

 large number of examples belonging to the same species and 

 examined in succession, are so many characteristics which 

 hinder our confounding it with the other elements of the 

 body. Its colour is always of a bluish-grey, while that of 

 the ovary is constantly of a dirty yellow, more or less con- 

 spicuous,; especially after treatment by acetic acid — a circum- 

 stance perhaps associated with a different chemical composi- 

 tion of the substance which forms the mass of the two organs. 

 Concentrated acids and very dilute alkaline solutions readily 

 dissolve it. Iodine tinges it yellow, and a very weak aqueous 

 solution of carmine, previously dissolved in ammonia, im- 

 parts to it pretty quickly a colour far more intense than that 

 of the solution itself.^^ 



There is little constancy in the relative position of the re- 

 productive organs among the various forms of Infmorla. 

 The testis may be either situate about the middle region of 

 the ovary, or nearer one of its extremities. 



" The figure of this little body is often perfectly globular, 

 at other times more elongated in one direction than in the 

 other, or like a grain of barley, the pip of an apple or raisin, 

 &c. This form becomes modified at certain periods, that is 

 to say, when the animal multiplies itself by fission or sexual 

 reproduction." 



The careful examination of the nucleolus in the enlarged 

 condition which it exhibits at these periods has led M. 

 Balbiani to the discovery of one or two curious peculiarities 

 in its structure. " Such (he writes), are the striae which it 

 presents on its surface before fission ; striae which I attribute- 

 to the existence of ridges or thickened portions of tLc outer 

 membrane, rendered more distinct by the increase of size 

 referred to above. These ridges may readily be separated 

 from one another by crushing the organ, and tbey then show 

 themselves as parallel, fusiform rods, slightly curved, from 

 •1 to *3 mm. in length, io^^ in number, and following the 

 direction of its greater axis. This fibrous structure of the 

 testis, little, if at all, visible at other periods of the year, 

 makes its appearance contemporaneously with the first stage 

 of its evolution at the sexual epochs, and might be mistaken 

 for a development of seminal corpuscles. But these do not 

 appear until afterwards, and give rise to a far more delicate 



