232 Miscellaneous. 



bears towards its posterior extremity, which is obtuse, four appen- 

 dages — two very small ones in the centre, and two larger at the 

 sides. 



After its escape from the ag^, when free in the water, where it is 

 at first called upon to live, the embryo of the GonUl has not at its 

 command any great means of locomotion. Its cj'lindrical and not 

 very mobile tail cannot serve it for swimming. At the utmost it 

 might make its way through the mud by means of the hooks with 

 which its retractile head is armed. It must also be easily carried 

 along by even the weakest current. Those which I kept in glass 

 vessels finally adhered to the walls, and formed there, by their 

 number, a sort of pulverulent coating. In the natural state they 

 must fix themselves in the same manner to pebbles and the roots 

 and stems of aquatic plants ; and it is there that they lie in wait for 

 the larvae of which they are the predestined parasites. 



This is not an hypothesis ; for the experiment has been made. 

 Having placed a certain number of the embryos in the presence of 

 various larvte of culiciforni Tipularia (Oorethra, Tani/pus, Chirono- 

 mus), I have had the satisfaction of seeing them encyst themselves. 

 The little worm penetrates into these larva), whose integuments are 

 but slightly resistant, by means of its cephalic armature, which it 

 causes at first to project suddenly ; its prickles becoming reversed 

 catch in the tissues of the larva, fix themselves there, and allow the 

 trunk to bury itself deeply : then it withdraws the whole, to recom- 

 mence the same manoeuvre. As soon as the embryo has found a 

 resting-place to suit it, it remains motionless ; then the fluids which 

 bathe it all round become coagulated and form for it an investment 

 which, by hardening, becomes a true cyst. Tiiis cyst, the outer surface 

 of which seems to be covered with small irregular concretions, is at first 

 transparent and exactly applied to the embryo ; but if we reexamine 

 it in a few days, we find that it has become brown and elongated, 

 and tliat the embryo only occupies the anterior part of it, which 

 probably is never completely closed. Thus the little parasite, after 

 its encystation, still travels in the tissues of the larva, constantly 

 elongating its cyst and leaving behind it an emptj^ space, which 

 becomes larger and larger, until the moment when itself passes into 

 the larval state. Such are in fact the conditions of its existence ; and 

 such is the use of the complex armature which it has received from 

 nature. 



The Gord'd are therefore subject, in tlie course of their develop- 

 ment, not only to necessary migrations, but also to complete metamor- 

 phoses. This fact, which we were far from anticipating, shows that, 

 as regards the first phases of evolution, there is no analogy between 

 Mennis and Gordlus, and that the latter, in the embryonic state, have 

 a certain resemblance to the Acanthocephala. — Comptes Rcndas, 5th 

 August, 1872, p. 363. 



