LEUCKART, ON PENTASTOMUM TANIOIDES. 191 
that species represents the young condition of Pentastomum 
tenioides. 
With the establishment of this fact, our knowledge of the 
life-history of the parasites in question has certainly been con- 
siderably advanced, though by no means brought to a con- 
clusion. Before we can boast of this, the question of the 
developmental history of Pent. denticulatum must be first 
fully solved. 
The embryos of P. tenioides exhibited structural condi- 
tions which are remarkably different from those of Pent. 
denticulatum, but in what manner and under what conditions 
these differences are equalised, is as yet completely unknown. 
In my first communication respecting Pentastomum den- 
ticulatum, I have suggested that, aceording to older observa- 
tions incidentally made, the ova of P. tenioides, which are 
ejected with the nasal mucus, might be accidentally in- 
troduced into the food of rabbits, and then swallowed by 
these animals. It was further assumed that the egg-shells 
are dissolved in the cavity of the stomach by the influence 
of the gastric juice; that the embryos being set free, pierce 
the intestinal walls, enter the various organs, and are there 
developed, under favorable circumstances, into the well- 
known form of P. denticulatum. This hypothesis was partly 
founded on the organization of the embryo and the cha- 
racter of its egg-coverings, partly also upon the analogy 
with other helminths, especially the Tzeniz, whose eggs and 
embryos exhibit similar relations. Besides this, I had on a 
previous occasion tried in vain to make the embryos of these 
animals escape from the egg by keeping them for some time 
in water. 
The correctness of this hypothesis had now to be tested 
experimentally. For this purpose, on the very first day of 
the last investigation (August 25th), I fed eight rabbits with 
ova containing mature embryos taken from my three female 
Pentastomata. 
Two of these rabbits were destroyed within the next few 
days. I had hoped to surprise the young embryos in the act 
of migrating in the interior of their host, but my experiments 
in this direction unfortunately failed; partly, perhaps, be- 
cause, being still uncertain of a favorable result, I did not 
devote myself with that perseverance which is necessary in 
such delicate matters. Nevertheless, I scarcely doubt that a 
repetition of these researches will repay the trouble, for the 
discovery of the embryonic Pentastomata is certainly less dif- 
ficult than that of the six-hooked embryos of the tape-worm, 
which are much smaller. The differences of size between 
the two kinds of embryo are so marked that they perhaps 
