History of the Nematode Worms. 457 
foundation: even now it can only be regarded as question- 
able. 
I know the embryos of Filaria medinensis from my own exa- 
minations, and can assert that they furnish no point of support 
for Carter’s hypothesis. They are especially destitute of that 
peculiar development of the rudimentary sexual organs which 
appears so strikingly in the embryos of Ascaris nigrovenosa, and 
as it were foreshadows the remarkable destiny of this worm. 
To this may be added that the embryos of Filaria have been 
kept alive in water for a considerable time without change, by 
different observers. 
If I were to put forward a supposition with regard to the 
destiny of these embryos, it would be to the effect that they are 
destined to an active immigration. I found this especially upon 
the considerable development of the tail, and the similarity which 
they present to the embryos of Cucullanus. The latter goes so 
far that one might easily be led to confound the two forms with 
one another, although the proportionate sizes do not exactly 
coincide. But it must be left to the future to decide whether it is 
the definitive host into which the embryos penetrate (through the 
sudoriferous pores, as Carter supposes), or an intermediate host, 
which is then probably mtroduced into the stomach. Indeed 
there are numerous surgeons who, in spite of all apparent rea- 
sons to the contrary, suppose the Filaria medinensis to penetrate 
into the muscles from the intestine. 
On the other hand, and from the analogy of Ascaris nigro- 
venosa, | think I may accede to Bastian’s supposition, that the 
embryonal development of Filaria medinensis takes place without 
the concurrence of male individuals. Hitherto no male example 
of this parasite has ever been found; and yet, although it is no 
doubt smaller than the female (considering the enormous fer- 
tility of the latter), it could hardly be overlooked on account of 
its size. The same consideration also excludes the supposition 
that the Filaria, although its size when seeking its definitive 
dwelling-place will be but small, has already received its store 
of seminal fluid. 
Unfortunately I must here admit that my investigations upon 
the Nematoda of man present many other gaps. And yet, of 
course, the fate of these parasites is of the greatest importance to 
us. I can, however, add something even about these animals. 
I may state, in the first place, that most of the Nematoda of 
the human subject belong to the species with hard and firm 
egg-shells. This applies especially to the more abundant spe- 
cies, Trichocephalus dispar, Ascaris lumbricoides, and Oxyuris 
vermicularis. The ova of the last-mentioned worm contain an 
embryo at the period of their escape from the female organs ; 
