336 ON THE SPERMATOZOA OF PETROMYZON.  [Apr. 20, 
4. Sketches of the Spermatozoa of Petromyzon. 
By Grorce Guiiiver, F.R.S. 
[Received April 7, 1875.] 
In my paper “‘On certain Points in the Anatomy and Economy 
of the Lampreys,” published in 1870 (P. Z.S. 1870, p. 844), there 
is an engraving of the spermatozoa of Petromyzon planeri. But I 
know not that those of P. marinus have ever been described or 
depicted ; and as they differ curiously in the two species, sketches of 
them are here given. 
chars SN 
par aN : 
4000 ths, 1 1 1 1 ! of an Tueh 
Fig. 1. Spermatozoa of Petromyzon marinus; fig. 2. Spermatozoa of P. planeri. 
The scale is divided into ten parts, each one of which stands for zo'5q of an 
English inch. 
The spermatozoa of P. marinus, notwithstanding the great size of 
the species, are much the smallest, and have a distinct and rounded 
head. Their mean length is about 3,4, inch, and their thickness 
astyz: They were obtained from a fish 32 inches in length and 
three pounds in weight, taken on the 12th of May, 1874, in the river 
Stour, near Sturry Mill, about two miles below Canterbury. The 
milt, which distended the whole abdomen from the pericardium to 
the anus, was a soft pulpy mass chiefly composed of a creamy semen, 
and so rich in, and crowded with, spermatozoa of such minuteness 
that they were with difficulty distinguishable ; and it was not before 
the semen had been much diluted and placed under Powell and Lea- 
land’s 51, objective that a good view of them was obtained. Under 
a lower power, especially in the pure semen, nothing more than con- 
geries of indistinct rounded points appeared, like those which I 
have described in the ‘ Proceedings’ of this Society (P. Z.S. 1842, 
p- 99), as the “ molecules of the semen.” In short, unless great care 
be taken, the spermatozoa in the ripe testis are so very faint, minute, 
and abundant, that they are likely to escape detection. 
But the spermatozoa of the little Petromyzon planeri are much 
larger and more easily seen. They are club-shaped, without a di- 
stinct head, and have an average length of 5,4; inch, and a thickness 
of s54y5- They were obtained in April from a fish 6 inches in 
length and 2 drachms in weight. Further details concerning the 
generative organs of both sexes are given in the paper first quoted 
in the present communication. 
