28 E. Eay Lankester, on the Gregarinida. 
ably abundant in the very common Nemertians^ Ommatoplea 
gracilis and 0. rosea. 
M. pellucida, Koll._, Nereidis, Leidy. — In Nereis pelagica 
I observed several fine Gregarinida in the intestinal canal 
(figs. 4^ 5). Kolliker^s M. pellucida appears to be a young 
form of this same species^ since he obtained it in Nereis and 
observed its paucity of granules and small size. The larger 
individuals which I have observed have a very dense mass of 
fine granules, which_, however, does not appear to occupy so 
much of the cavity as is usual. There is a broad semi- 
transparent margin of contractile sarcodic substance, which 
appears to give this species a greater activity than is observ- 
able in other well-grown forms. The vesicle is small, but 
clear and conspicuous ; the largest specimens noticed had a 
length of -rrot^^ of inch. 
M. Eunicce, n. sp. — In the intestine of Eunice Harassii I 
noticed the Gregarina drawn in fig. 10. Its length was -yito^^ 
inch ; the contained granules were coarse, and the tunic was 
produced posteriorly into a somewhat pointed wedge-shaped 
body. 
M. Phyllodocce, Claparede. — M. Claparede figures Grega- 
rina from Phyllodoce in his ' Recherches sur les Annelides, 
Turbellaries, &c.^ The form, however, which I observed in 
several species of Phyllodoce diff'ers much in appearance from 
that which he figures (fig. 12). Its usual length was -rhro^^^ 
of an inch, the granules pale and indistinct, and the vesicle 
elongated. 
It is extremely difficult to point out any characters by 
which any two of the forms of Gregarinida above noticed 
could be distinguished, excepting as regards that found in 
Nereis, which differs materially from the others. There are, 
however, small indications in the general appearance and 
habit of these creatures which at once appeal to the observer, 
and enable him to recognise some of the more dubious 
species as distinct from each other. I was thus easily able 
to recognise the Monocystis of Ommatoplea when occurring 
in the intestine of Aphrodita hystrix without any hesitation ; 
the sea-mouse had probably taken it in with food, since Turbel- 
larians are remarkably common in the same locality in which 
the Aphrodita occurs. It is a fact worth noting, that only 
one instance of this was observed in various examinations of 
more than thirty specimens of Aphrodita. Aphrodita aculeata, 
which has a peculiar form of Monocystis,"^ did not occur off 
Guernsey. 
* ' Quart. Journ. Mic. Science,' April, 1863. 
