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 ail 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 vesiculge 
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, I 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 
* Wagner and Leuckardt, loc . cit . p. 508. 
2 M 2 
