192 LEUCKART, ON PENTASTOMUM TZAENIOIDES. 
influence the direction which the wanderers select in the 
body. This much at least is certain, that if the embryos of 
the Pentastomata follow the circulation of the blood, like 
those of the Tzenioid worms, it can only be when they obtain 
access to the larger vessels. 
[Here follows in the original the detailed account of several 
observations on the earliest condition of the larval Pentusto- 
mum, which it seems hardly necessary to give at length; and 
we shall therefore conclude with the author’s summary of 
the results of his experiments and researches. 
These, he says, may be comprehended under some such 
laws as the following: 
1. That the entozoon known under the name of Penta- 
stomum tenioides from the nasal cavity of the dog and wolf, 
passes the early stage of its existence in the interior of the 
rabbit and other mammals, especially in the lungs and liver 
(occasionally also in man). 
2. The development of Pentastomum tenioides takes place 
under a simple metamorphosis, and presents four successive 
phases : 
(a) The condition of the Pentastomum-embryo, furnished 
with a boring apparatus and claw-feet. 
(2) The condition of the encysted and immotile Pentasto- 
mum (the pupa state). 
(c) The condition of the so-termed Pentastomum denticu- 
latum, with a crown of spines and double hooks, one of which 
is moveable (the larval condition). 
(d) The condition of the sexually mature Pentastomum 
tenioides, with simple moveable hooks and without a crown 
of spines. 
3. The time occupied in the development of Pentastomum 
tenioides is nearly a year—the larger portion of the period 
being taken up in the formation of the larval form (Pent. 
denticulatum), and the remainder devoted to the trans- 
formation into the sexually mature animal (P, tenioides). 
The male reaches maturity earlier than the female. 
4, The embryo and larva, possessing special provisional 
motile organs, are organized for an active migration; and 
consequently are in a condition either to change their posi- 
tion in the interior of their host, or to pass from one host to 
another. 
5. The first migration of these parasites is passive, mas- 
much as the ova containing mature embryos issued into the 
outer world contaminate the food of other animals in com- 
pany with which they are conveyed into the stomach, 
