THE ORTHONECTIDA. 
237 
are of a nature to make one very cautious on this subject ; 
but, in addition to the special characters of the histological 
constitution of the ectoderm, I have recently observed new 
facts which still further separate Intoshia gigas from Mliopa- 
lura ophiocomce. 
It appears, as the result of an examination of many 
hundreds of adult individuals, that Intoshia gigas never has 
its non-ciliated segment provided with papillae, nor even 
with refringent corpuscles. The refringent corpuscles’^ of 
M. Metschnikoff form actual projections on the ring, which 
I call the “ papilliferous ring ” in Rhopalura. It must, 
then, be admitted that if such corpuscles exist in the sup- 
posed females of the parasite of Amphiura squamata, this 
parasite belongs to a new species (as is probable enough a 
priori)^ and that the sexual dimorphism is less accentuated 
ill this species than in the other. 
VIII. — Phylogeny. 
With reference to the position of the group of the Ortho- 
nectidaon the genealogical tree of animals, it is very difficult 
to make a definite statement. But there is no doubt that 
these parasites ought to be attached to the phylum of the 
Vermes, and take their place at the base of this phylum side 
by side with the Dicyemida. The phylum of the worms 
would then, according to my idea, be represented by the fol- 
lowing diagram : 
Cestoda, 
Turbellarta, Trematoda, 
L . J 
Gastbrotricha, Prothelmintha, Dicyemida, 
Orthonectida, 
Gastrseada. 
The Orthonectida must occupy in this scheme an inferior 
position to that of the Dicyemida. These latter are evidently 
much degenerated by parasitism. Their organisation must 
have been formerly much higher than it is to-day. The 
epiderm contains very clearly [Dicyema of Sepia) the rod- 
like bodies characteristic of the skin of the Turbellaria, and 
the embryo presents a very complex organ, the ur?ia : nothing 
of this sort is seen in the Orthonectida.^ One of the most 
^ See on “ Dycyemida,” the beautiful memoir of Edouard Van 
