30 ON MYORYKTES WEISMANNI. 
the vermicules were 1:162 mm. long and 0°162 mm. broad, 
they had in June attained a length of 0594 mm. and a breadth 
of 0°189 mm. But excepting the reproductive organs, no 
other parts at this time exhibited any special change. These 
organs contained at this time, together with young germs, 
instead of the minute ova, one or two larger ones, 0°06 mm. 
long and 0:0108 wide, and of an elongated form, and consist- 
ing of an extremely delicate membrane and a vitellus con- 
taining several oil-globules, and surrounded, as it seemed, by a 
very delicate vitelline membrane. Sometimes, though rarely, 
these ova were found in the primitive fibres. At this season 
males were never observed, nor could any zoosperms be 
seen in the females. From this circumstance, as well as from 
the occurrence of the larger oil-globules in the vitellus, it 
would appear that the ova were unimpregnated. On this 
account, and owing to the small number of ova met with 
(about four), the author did not attempt any experiments in 
the way of transplantation. 
Having communicated his first observations, made in 
March, to Professor Leuckart, the author learnt from him 
that, as far back as in 1861, Dr. Weismann, of Frankfort, 
had noticed a nematode worm in the rectus femoris of Rana 
temporaria, which corresponded in every particular with his 
description. In confirmation of this, Professor Leuckart also 
forwarded Weismann’s original drawing, which left no doubt 
as to the identity of his worm with that described in the 
present paper, notwithstanding the existence of some apparent 
differences in the minor details. 
From what has been said, it will be seen that the new 
parasite differs from Trichina spiralis both in structure and 
habits; and, as far as can be judged from Mr. Bowman’s 
figure (Phil. Trans.,’ 1840, p. 480), in outward appearance it 
bears no resemblance to the nematodes found by him in the 
primitive fibre of the muscles of the eel, and Mr. Bowman 
gives no details respecting the structure, &c. The two are, 
however, allied in this respect—that both appear to reach 
sexual maturity in the muscle. 
The muscular tissue itself does not appear to suffer any 
injury from the presence of its guests, which are nourished, 
not at the expense of the muscle, but probably only by the 
fluids with which it is pervaded. 
In this respect it would appear to differ, so far as its effect 
upon the muscular tissue is concerned, from both Trichina or 
Gordius, whose invasion is eventually, at any rate, attended 
with destruction or injury to the muscular substance forming 
their nidus. 
