78 SURVEY OF THE REPRODUCTIVE PROCESS 



same direction, and the two mouths closely applied to each 

 other. In this state the two conjugated individuals con- 

 tinue moving with agility in the liquid, and turning con- 

 stantly round their axis.* There is nothing before copula- 

 tion to announce the evolution of the sexual elements ; it 

 is during the act itself, of which the duration is prolonged 

 for five or six days, or even longer, that their development 

 takes place, at the expense of the nucleus and nucleolus of 

 each animalcule. The nucleolus undergoes a considerable 

 increase in size, and becomes converted by sub-division into, 

 two or more capsules, which contain ultimately minute 

 fusiform bodies with fine filamentous extremities, regarded 

 by Balbiani as spermatozoa. The corpuscules, which he 

 considers as of a germinal nature, are certain spheroidal 

 bodies, with indistinct central spots, formed in the sub- 

 stance of the nucleus with or without its previous segmen- 

 tation. Fecundation seems to be effected by a transference 

 of one or more of the spermatic capsules, through the closely 

 adpressed mouths, from the body of one animalcule into 

 that of the other. They continue to increase in size after 

 their transference has taken place, one only arriving at ma- 

 turity at a time. Five or six days after copulation, minute 

 rounded germs make their appearance, and in the course of 

 development are extruded from the body of the parent 

 animal, but for some time after this they remain adherent 

 to its exterior by means of the knobbed tentacles or suckers 

 with which they are provided. At length they detach 

 themselves, lose their suckers, acquire a mouth in their 

 stead, and, becoming furnished with vibratile cilia, take on 

 the aspect of adult Paramcecia.^ 



* In a second communication Mr. Balbiani generalizes his conclusions, 

 and extends them to several other Infusoria, as Euplotes, CMlodoii 

 Spirostomum, and Oxytrichina. Annals of Nat. Hist., 3d Ser., II., 440. 



f Dr. A. Thomson in Cyclop. Anat. and PhysioL, Art. Ovum, p. 7. 

 Greene's Protozoa, p. 51-71. 



