THE ORTHONECTIDA. 
233 
spending cell of adjacent rows, so as to form a longitudinal 
series. It is to this disposition that the longitudinal striae 
observed by Macintosh are due, which led this naturalist 
to approximate the parasites of Lineus to the Opalinae. 
The ring a contains three rows of cells, the ring j3 com- 
prises two, the ring y only one, and the others only one. 
The ectodermal cells oilntoshia gigas are, accordingly, much 
smaller and much more numerous than those of Rhopalura, 
All the cells, without exception, have long cilia. The head 
carries, as in Rhopalura, a bunch of straight cilia directed 
forwards. This character is, in fact, common to all known 
species of Orthonectida. 
The endoderm forms a regularly ovoid sac, constituted in 
the adult animal by beautiful polygonal cells, and enclosing, 
in its interior, other cells of a rounded shape, more or less 
abundant. 
The action of acetic acid is such as to detach the ectoderm 
(PI. XXII, fig. 7), and then brings well to view the endo- 
dermic sac. The jerking movements of the caudal part are 
much less energetic in Intoshia than in Rhopalura, We 
should, therefore, expect to find the muscular system much 
reduced ; and this is actually the case, and for a long time I 
in vain endeavoured to see the muscular bands at all. I 
succeeded, however, last summer by producing a gradual 
and very slight compression of the animal by allowing the 
water to evaporate from beneath the cover glass. The 
bands were rendered visible at the anterior part of the 
body, where the endodermic cells hinder observation the 
least. The bands have the same oblique direction as in 
Rhopalura. 
V. — Gemmiparous Reproduction of the Orthonectida. 
The oldest individuals of Rhopalura or of Intoshia pre- 
sent a considerable modification of the endodermal cell- 
layer. The cells of this layer are no longer visible, and the 
endoderm seems formed by a homogeneous membrane of 
granular aspect, very similar to certain tissues of the Nema- 
toids. On the other hand, we have seen that the ectoderm 
can be detached in these animals with the greatest facility 
under the influence of reagents. As a result of the pro- 
liferation of cellular elements in the interior of the endo- 
dermal sac, this organ swells, becomes spherical, and burst- 
ing the ectoderm, which disappears, is transformed into a 
true sporo-cyst ” (PI. XXII, figs. 14, 15, 16 and 17). In the 
interior of the sporocyst are seen buds, the cellular nature 
of which is extremely difficult to demonstrate. The same 
