AND ON THE DIRECT AGENCY OF THE SPERMATOZOON, 237 
hours. But this time may differ in different species of the Anoura, and of the higher 
vertebrata, and may have some relation to the particular economy of each animal. 
The general conclusion which seems to be deducible from a comparison of the 
observations of Spallanzani and of Prevost and Duimas, with those by myself, in 
regard to the tail-less Amphibia, is, that — making allowance for the difference of 
species and habit of the animals experimented on, and for the degree of maturity of 
the fluid, which there seems reason to think does not attain its perfect condition 
until it has passed into the efferential ducts and vesicles — the vitality of the sperma- 
tozoon, and the duration of its fecundatory power, are in a ratio inverse to that of an 
increase of temperature in the surrounding medium. 
2. EVOLUTION OF VITALITY IN THE SPERMATOZOON AND OVUM. 
Wagner and Leuckardt have already pointed out* that the power of motion 
possessed by the spermatozoon is closely connected with the completion of its struc- 
ture and composition, and is gradually evolved as the development of this body 
proceeds. This power of motion 1 shall presently endeavour to show I regard as the 
visible exponent of its fecundatory force, or form of vitality, and that a similar power 
is evolved concurrently with this in the spermatozoon in the contents of the egg, the 
evolution in both being more or less influenced by temperature, according to the 
species. These facts are well shown both in the Frog and Toad. 
Several pairs of Frogs were collected on the 2nd of March, when the temperature 
of the season was low, and strong easterly winds prevailed, during which Frogs 
seldom spawn, except in very sheltered places. As one female had passed some eggs, 
and believing that the others were equally advanced, I selected a pair, which 
appeared to be the most mature, for experiment. The fluid from the male was 
obtained with the greatest ease, in full quantity of a white and somewhat opake 
colour. When examined with the microscope it was found to consist in chief part of 
developmental cells, containing each its motionless immature spermatozoon. Besides 
these cells it also included many others less far advanced, and in which I was unable 
to distinguish this body. In addition to these there were some also from which the 
spermatozoa were in the act of being liberated, besides many very active spermatozoa 
already set free. These constituted nearly one third of the whole mass. It was 
evident from these circumstances that the fluid was immature, and not fitted for 
experiment. Five days afterwards, March 9th, I again examined fluid from this 
male, which had been kept since the previous examination, in a separate vessel, so 
that there was no mistake in its identity. The mean temperature of the room during 
the interval was 42*°5 Fahr,, and the water in which the Frogs were preserved 
40° Fahr., but none of the Frogs had spawned. The fluid was then less dense and 
of a less white colour, and was composed almost entirely of very active and fully 
developed spermatozoa, with but very few cells from which these bodies had not 
* Article “ Semen” in Cyclopaedia of Anatomy and Physiology, part xxxvi. (January, 1849) vol. iv. p. 504, 
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