ON THE DEVELOPMENT OF ASCARIS NIGROVENOSA. 103 
not always successful, but sufficiently often to show that the 
lungs are the true destination of the embryos, which, if 
swallowed, invariably perish after a time in the stomach. 
Professor Leuckart has carefully traced the development of 
the embryos into the perfect A. nigrovenosa in the frog’s lung, 
and has found that they are all invariably females, so that 
there can be no doubt that the production of young in the 
parasitic Ascaris is entirely parthenogenetic. It is beyond 
doubt also, he says, that this mode of parthenogenesis is 
widely diffused among the nematodes, and cites as a tolerably 
certain instance of it the case of Filaria medinensis. With 
respect to which species, he remarks, that from Carter’s 
observations, it would seem probable that Filaria medinensis, 
like A. nigrovenosa, exhibits two kinds of generations — 
a parasitic and a free, and that thus it would present an 
exact analogy with the parasite of the frog’s lung. 
He is of opinion, however, that this notion is erroneous. 
And he is led to think so from the circumstance not only of 
the slight degree of development of the embryonal rudimental 
reproductive system, but further, from the striking similarity 
between the embryos of F’. medinensis and those of Cucullanus 
elegans. According to all analogy, the embryo of F. medinensis 
is equally destined to migrate as is that of Cucullanus, 
though whether this migration is confined to the human 
subject or not it is impossible to say. 
At present, he says, notwithstanding his pretty extensive 
experience on the subject of the developmental history of the 
Nematoda, that of Ascaris nigrovenosa stands alone. 
On this account it is the more interesting to record the 
same phenomena in other groups of the lower animals, 
amongst which he notices the extraordinary fact discovered 
by Hackel, of the production, within the visceral cavity of the 
mature Geryonie, by a process of budding, of Medusoids of 
quite another organization (Cunine), which also in their turn 
reach sexual maturity. He adverts next to the life-history of 
Coccus formerly described by himself.* In this case, as in 
A. nigrovenosa, two successive generations of different kinds 
are thrown off, both of which become sexually developed, 
and both of which exist under different conditions. It is true 
that the vital conditions in the Aphis-like winged and the 
Coccus-like wingless generations are not so strikingly dif- 
ferent as in A. nigrovenosa ; but the difference between the 
two cases is only one of degree, and as such points distinctly 
enough to the analogy which exists between them. It is 
remarkable, also, that in Chermes the dimorphism of the suc- 
* © Archiv f. Naturgesch,’ 1859, p. 208. 
