KKPKODUCTIOX IX THK INFUSORIA. 189 



to ask liimself the question, does the mouth itself act the 

 part of a genital duct ? This he was the more disposed to 

 answer in the affirmative, from having once, as he thought, 

 seen a seminal capsule entangled in the buccal cavity of one 

 or two copulating individuals. But further researches failed 

 to bring confirmation. At length his patience was rewarded 

 by the actual discovery of what appeared to be true sexual 

 apertures in several distinct forms of the class. 



In a pair of copulating Paramecium aurelia a distinct ex- 

 cretory duct, was s*een to run from the ovary and testes of 

 each, to a point just above the mou.th, towards the posterior 

 end of the buccal depression. Whether these two ducts were 

 furnished with orifices of their own, or together opened into 

 the same cloaca, INI. Balbiani could not exactly determine. 

 Such an orifice, he thinks, must exist under the form which that 

 of the digestive apparatus presents in many Infusoria, among 

 which, except while feeding, the sides of the mouth are so closely 

 apposed to one another, that the very existence of this aperture 

 remains for a time doubtful, until, in fact, the special stimulus 

 of food causes its dilatation. Of this nature is the generative 

 orifice of the Oxytrichina, though the canal which serves to 

 connect it with the reproductive organs, has not as yet been 

 satisfactorily determined. In Trachelius ovum, however, all 

 parts of a very complete genital system are clearly discernible. 

 As in Paramecium aurelia there are two distinct ducts, which 

 connect the ovary and testis with a well marked aperture situate, 

 like that of the Oxytrichina, in front of the mouth. The layer 

 of cuticle which clothes the general surface of the body, stops 

 short just before reaching the margin of the aperture, so as 

 to leave exposed a projecting rim of granular tissue, which, 

 in its various states of construction, causes the orifice itself 

 to vary much in form, so that, occasionally, two distinct 

 apertures appear to be present. 



In Stentor, also, and especially in S. cceruleus, when the 

 body is fully extended, a cleft like that of the Oxytrichina, 

 may be noticed on the depressed region of the cleft sur- 

 rounding the mouth ; and, by the margins of this cleft,as 

 well as throughout a certain extent of the oral depression, 

 two of those animalcules have been seen to unite in copula- 

 tion. But, the mouth itself takes no part in this act, so that 

 the pair of conjoined Infusoria continued to feed as before, 

 while in such forms as Paramecium aurelia feeding becomes 

 impossible, by reason of the close apposition of their two 

 mouths during the period of sexual contact. 



Seeing, therefore, that a genital orifice appears in several 

 varied forms of the class, it might be inferred that it exists in 



