MECZNIKOW, ON ASCARIS NIGROVENOSA. 29 
represents a slender elongated organ, dilated at the extremity. 
The intestine continued from it is straight and cylindrical, 
with a contracted calibre. The anal orifice is placed in the 
hinder part of the body. The sexual rudiment of these larvie 
is placed in the middle of the body, and is of very inconsider- 
able size. 
The habits of the above-described larve differ from those 
of their parents in the circumstance that they are normally 
aquatic, and are capable of performing extraordinarily rapid, 
serpentine movements. 
In this condition the larve live for an indefinite time in 
the mud without undergoing any change whatever, until they 
have entered the body of the frog.* When small frogs 
(especially the green frog) are fed with the mud in which the 
new generation of Ascaris nigrovenosa has been developed, 
the larve are afforded an opportunity of making their 
entrance into the lungs. When they have reached this 
locality they cast their skin for the first time, and at the 
same time some other changes will be observed to take place. 
The old longitudinally-striped cuticle is now cast off, in con- 
sequence of which the tail appears much blunter than before. 
The head, after the ecdysis, presents minute projecting lips 
encircling the oral orifice. In individuals in this condition 
the excreting orifice is also apparent, as well as a differentia- 
tion of the future muscles, which at this time consist of an 
exterior homogeneous and an internal granular layer con- 
taining cell-nuclei. 
During their abode in the frog’s lung the larve increase 
considerably in size. On the fourth day of their parasitie cxist- 
ence the author has noticed some already well-grown larvee in 
the act of their second ecdysis, but unfortunately was unable 
to preserve them alive sufficiently long to allow of drawings 
being made from them. Eight days after the migration of 
the young larve into the body of the frog he observed 
these parasites in a further stage of development. Their 
length is now about 1°25mm. The oral orifice snrrounded 
by minute lips leads iuto a cavity furnished with chitinous 
walls. The succeeding csophagus, like that of the fully 
developed Ascaris nigrovenosa of the frog’s lung, exhibits 
only a terminal enlargement, and in the interior, granular 
transverse streaks and clear cell-nuclei. The intestine of 
* The mediation of the fresh-water molluscs in the transmigration of the 
Ascaridan larvee into the frog, which from the earlier observations on this 
subject (Leuckart, |. c., p. 229) was deemed to be requisite, has been shown 
to be unnecessary, since the larve are able to effect a direct entrance by 
themselves. 
