100 
Wagner in the semen of some Mammalia, and the “ apparently 
spherical and dense particles” observed by Dr. Davy (Researches, 
Physiological and Anatomical, vol. i. p. 332) in the fluid of the hu- 
man testicle, and which particles he conjectures may be the ova of 
the spermatozoa, are perhaps identical with the molecules of the 
semen. They are commonly rather smaller than the particles of the 
supra-renal gland. I have made many measurements of the mole- 
cules of the semen, and find them generally to be 1-20,000th of an 
inch in diameter, but almost always varying from 1-35,000th to 
1-8000th, and of course not at all approaching in size and other re- 
spects to the well-known corpuscles and cells of the semen. The 
molecules, especially those of larger size, refract the light strongly ; 
the smaller ones appear dark and opake in the centre when the 
focus of the object-glass is elongated, and bright and transparent 
when the focus is shortened; while the smallest of all, like those 
of the supra-renal gland, often seem quite black or opake, and ex- 
hibit very lively vibratory motions, particularly when diluted with 
water or acetic acid. 
That the molecules are connected with the perfecting of the se- 
men, would appear from the fact that they are most abundant in 
birds and reptiles when the testicles begin to enlarge, and either 
wholly disappear or become scanty as soon as the testicles are per- 
fectly ripe and the spermatozoa most completely evolved. But very 
minute vibratory particles are often observable in the seminal tubes 
of foetal animals. 
The figure of the molecules, like that of many other particles 
equally small, is apparently spherical, and, as already mentioned, 
they may present either a dark or bright central spot. But, as no- 
ticed in the Atlas to Gerber’s Anatomy, p. 59, it is difficult to de- 
termine the exact shape of particles so exceedingly minute ; and the 
elaborate researches of Dr. Barry (Phil. Trans. 1841, part 2) have 
rendered it probable that some of the particles which I have formerly 
mentioned (Appendix to Gerber’s Anatomy, and London Medical 
Gazette for May and November, 1839) as ‘‘ minute spherules” and 
‘* spherical molecules,” are in reality discs. 
Pigment.—In the foregoing table the black and yellow colour of 
the testicles of certain birds is noticed. I have carefully examined 
the black matter of the starling’s testicles, and found it to be com- 
posed of very distinct pigmentary ramifications, made up of most 
minute particles, many of which, when floating in the field of vision, 
exhibit exceedingly active motions. In the winter the testicles are 
quite black, and the pigment, perhaps from the small size of the 
tubes, seems to be contained within them; but when the testicles 
are enlarged in the spring, they present a lighter or brownish white 
colour, from the accumulation of semen, and the pigmentary ramifi- 
cations are evidently situated in or close to the coats of the tubes, 
the boundaries of which may be easily seen with a common hand- 
lens to be marked out by the black pigmentary dots. 
Spermatozoa of the Cervide and Camelide.—Professor Wagner 
(Physiology, by Willis, p. 34) regards the spermatozoa as essential 
