1866. | Zoology und Animal Physiology. 445 
his own, published more than thirty years since. MM. Coste and 
Blanchard, however, defend the value of this part of M. Gerbe’s 
work. It appears that no one had previously studied the Phyl- 
losoma, and that the earlier observations had reference to a 
branchiferous disposition of the vascular system, while M. Gerbe 
has carefully described the vascular apparatus in these abranchiate 
Phyllosomatous larvee of Decapods. In his last note published, M. 
Gerbe gives the following among the conclusions to be drawn from 
his researches. It is not until the fifth or sixth moult which follows 
birth that the general form of the adult can be detected in the larvee 
of Podophthalmatous and Edriophthalmatous Crustacea, and it is to 
these transitory forms, so different from those of the perfect animals, 
that a crowd of false species, of false genera, of doubtful families 
belong, and even, in the case of Phyllosoma, an entire order which 
is spurious. With the exception of the lobsters, the larve of all 
genera are when born destitute of any branchial apparatus, and 
hence their respiration bemg tegumentary, the circulation is neces- 
sarily very different from what it afterwards becomes. None of the 
larvee ever present even rudimentary reproductive organs. 
The development and reproduction of the Nematode worms is a 
subject which has lately been receiving considerable attention. 
Professor Leuckart has been most successful in tracing the modifi- 
cations of several forms. Herr Mecznikow, who has been working 
in Professor Leuckart’s laboratory, discovered that Ascaris nigro- 
venosa, which inhabits the lung of the brown frog, produces larve 
which enjoy a free existence, i which they attain to a sexual 
development. This very remarkable discovery has been exciting 
some contention, inasmuch as both Professor Leuckart and his pupil 
are anxious to receive credit for it. The larva which exhibit this 
curious phenomenon differ considerably from their parents; their 
development was traced by keeping them in a watch-glass with 
moist earth, and a part of the contents of the rectum of the frog. 
By this manipulation many forms of Nematodes may be kept for 
study and observation, which would perish wien kept in pure water 
only. Professor Leuckart has carefully watched the development of 
the embryos produced by ova from the female larve, duly impreg- 
nated by the males, and has traced them into the perfect Ascaris 
nigrovenosa in the frog’s lung, and has found that they are all 
invariably females, so that there can be no doubt that the produc- 
tion 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 this species, it seems probable from Carter's observations that, as 
in A. nigrovenosa, there are two kinds of generations, a parasitic 
and a free, and if so, we should have an exact analogy with 
the parasite of the frog’s lung. ; 
