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Show 336 ON THE SPERMATOZOA OF PETROMYZON. [A.pr. 20, 4. Sketches of the Spermatozoa of Petromyzon. By GEORGE GULLIVER,. F.R.S. [Eeceived April 7, 1875.] In m y paper " O n 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. 1 \, 1 Dl^ \ A ' ;i iOOO'i*-£'*L• 1* vi" i I ' ' ' ' ' ' cf an Inch 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 i^V o °f" 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 40**0() inch, and their thickness 41^66. They were obtained from a fish 3*2 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 -jig- objective that a good view of them was obtained. Under a lower power, especially in the pure semen, nothing more than congeries 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 tbe 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 distinct head, and have an average length of -goVir inch, and a thickness of So o00. 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. |