AND ON THE DIRECT AGENCY OF THE SPERMATOZOON. 261 



or encounter of the spermatozoon with the ovum were sufficient, it might be expected, 

 as has been well remarked*, that the influence of the spermatozoon of any animal of 

 the same class would be competent to effect the impregnation of any species. 



Yet all the phenomena connected with the origin and death of the spermatozoon 

 seem to be in accordance with the view, that its motion is essential to its function. 

 Whatever be the relation of this motion to its peculiar faculty, it is evident that 

 motion is intimately associated with, and dependent on, its material composition, and 

 structural development. In the Frog, the spermatozoa are usually completed very 

 early in the season, when the animals begin to emerge from their hybernacula, in the 

 beginning or middle of February ; but, as we have seen, they only begin to pass into 

 the efferential ducts from the testicle, at the time when the pairing of the sexes is 

 commenced ; from which time, to that of spawning, a period of from ten days to a 

 fortnight or three weeks, according to the temperature of the season, they are more 

 fully matured, and acquire greater vibratory power, and are collected in the vesiculse 

 seminales for expulsion at the instant after oviposition. In the Toad the spermatozoa 

 are developed at a later period of the season, but at a relatively corresponding period 

 in the life of the animal. The male Toad, like that of the Frog, usually emerges 

 from its hiding-place a few days, or a week or two earlier than the female. I have 

 taken the males in the middle and at the end of March, at which time I have not 

 been able to detect any seminal fluid in their vesiculae seminales ; yet they are then 

 exceedingly salacious and disposed to pair, and I have sometimes found the contents 

 of the reproductive organs in a similar state, even after the sexes have been for two 

 or three days in union. The testicles, nevertheless, are then filled with an abundance 

 of spermatozoal cells in the course of development, and also with a great quantity of 

 spermatozoa, each still included in its vesicle of development ; but as yet immature, 

 motionless, and with only a very short caudal extension from its thick cylindrical 

 body. Besides these there are usually a few spermatozoa, more matured than the 

 rest, which exhibit movements while still retained within their cells, which are enlarged, 

 and from which they are soon to be liberated. 



Thus motive power in the spermatozoon is coincident with the completion of its 

 structure and composition, and as such, may fairly be regarded as essential to its 

 function. In the Frog the motion of the spermatozoon is most intense and persistent 

 at the full period of connubiality. On the other hand, 1 have constantly noticed in 

 all my experiments on artificial impregnation, that where impregnation has not been 

 effected, all the conditions being favourable to it, or when I have found by trial that 

 the male fluid has ceased to be efficient, that then nearly the whole, or perhaps all of the 

 spermatozoa, have been perfectly motionless, and apparently dead. This is also the 

 condition in which I have usually found the few spermatozoa which are retained in 

 the reproductive organs a week or two after pairing, when the male Frog and Toad 

 may be regarded as in the state of aged individuals, the season of reproduction 



* WAGNEB and LEUCKARDT, loc. tit. p. 508. 

 2 M 2 



