472 Miscellaneous. 



Vermes. My researches have been made upon Intoshia linei, para- 

 sitic upon a Nemertean, and upon two species parasitic upon 

 Ophiurans, Rhopalura ophiocomce and Intoshia gigas. 



The movements, independent of vibratile cilia, which I observed 

 in these parasites are due to the presence of musculoid bands 

 belonging to the endodermic cells, and forming a splanchno -pleural 

 pseudo-mesoderm, analogous to the somato-pleural pseudo-meso- 

 derm formed in the Coelenterata by the epithelio-muscular cells of 

 Kleinenberg and Korotneff. 



To the ensemble of these elements I give the name of pseudo- 

 mesoderm, because I think it right to reserve the name of mesoderm, 

 properly so called, for other formations, which do not exist in the 

 Orthonectida, and the homology of which in the various groups of 

 Metazoa is rather difficult to establish. I distinguish : — 



1. A solid mesoderm, formed very early at the expense of the 

 endodermic cells of the embryo (rudiment of the chorda of the 

 Tunicata and Vertebrata ; skeletogenic cells of the embryo of 

 Echinoderms ; mesodermic cells issuing from the four first spheres 

 of the endoderm of the Planar ice and of Boncllia, according to the 

 researches of 1\ Hallez, Sprengel, &c). 



2. A .cavitary mesoderm, formed by diverticula of the endoderm 

 (enterocceles) and appearing generally at a later period (aquiferous 

 system of the Echinoderms, enterocoele of the Tunicata, Brachiopoda, 

 Sagitta, Amphio.vus, &c). 



The solid mesoderm gives origin especially to the muscular 

 system ; the cavitary mesoderm principally forms the vascular 

 organs. 



The physiological function of a histological element, however, is 

 only of secondary importance in the determination of phylogenetic 

 homologies. A muscular element, for example, will always origi- 

 nate where the want of it is felt, whether in a rudiment of endo- 

 dermic origin, or at the expense of ectodermic elements (Nemer- 

 teans). It may even be formed from only a portion of a cell (plas- 

 tidule), as occurs in the Infusoria, the Coelenterata, and the Ortho- 

 nectida. 



The reproduction of the Orthonectida is effected in two different 

 manners : — 



1. Sexually. In different cases, there is formation of a blastula 

 which becomes laminated (Intoshia gigas), or production of an 

 epibolic gastrula which finally closes (Rhopalura ophiocomw). In 

 either case the result is a permanent ciliated planula with a meta- 

 merized ectoderm. The ectodermal metameres contain each a 

 single series of cells in Rhopalura and several series in Intoshia. 



2. By gemmiparity in the interior of enormous sporocysts, formed 

 by the endoderm of the progenitive animal. It is in consequence 

 of this gemmiparous reproduction that the Orthonectida are met 

 with in such great abundance in an infested animal. 



This double mode of reproduction approximates the Orthonectida 

 to the Dicyemida and other parasitic worms (Trematoda and Ces- 

 toda). Their more simple organization during the embryonic period 



