30 MECZNIKOW, ON ASCARIS NIGROVENOSA, 
individuals in this stage is an elongated tube with glandular 
walls, which runs straight to the rectum, and is always seen 
to be filled with reddish-brown contents consisting of the 
altered blood-corpuscles of the frog. The rectum, as usual, 
is represented by a slender canal, which opens on the ventral 
aspect of the body. At the point where it is continuous with 
the proper intestine, gland-cells of large size are placed; 
and cells of less size are also to be seen in the caudal pro- 
longation. 
In the above-described individuals will also be observed a 
peculiar granular gland lying on the ventral side of the 
anterior part of the body, and communicating by a duct with 
the excretory orifice. In the interior of this glandular body 
one or two cell-nuclei containing nucleoli will be seen. The 
nervous system at this period consists of an cesophageal ring 
and of two trunks, which become fused into the muscular 
layer. The muscles appear as completely developed fusiform 
cells. The strongly-developed lateral lines consist of closely 
contiguous cells 0°013 mm. in diameter, in which may be 
perceived a nucleus containing a large nucleolus 0:006 mm. 
in diameter. I have been unable to perceive any lateral 
vessels. 
All parasiticindividuals of Ascaris nigrovenosawhichtheauthor 
has had an opportunity of examining in the above-described 
stage of development have proved to be females. This cireum- 
stance speaks strongly in favour of the supposition thrown 
out by Leuckart (1. c. p. 230) that the parasitic female of 
Ascaris nigrovenosa is parthenogenetic.* The female gene- 
rative organs are double, and even at this stage exhibit a 
differentiation into ovary, vagina, and uterus. In the first of 
these three divisions large germinal vesicles, with a germinal 
spot 0°025mm. in diameter, are lodged. The vagina is 
represented by an elongated canal. 
All the observed parasitic specimens in the just-described 
stage were taken in the act of ecdysis, since the old skin could 
be seen raised up from the surface of the body. 
When the individuals inhabiting the frog’s lung just 
described are compared with the fully developed para- 
sitic Ascaris nigrovenosa, we shall be satisfied that the 
difference between them is only a gradual one, consisting as 
it does mainly in the greater size of the latter, and in the 
disappearance of certain internal organs. On this account, 
the want of observation of the later intermediate stages be- 
comes of less consequence. 
* It is equally favorable also to the view expressed by ourselves in 1846, 
that the parasitic guinea-worm was a parthogenetic female.—G. B. 
i ee ee es, ee he ee 
