E. Ray Lankester, on the Gregarinida. 25 
Large size of some species. — It appears that the Monocystis 
Lumbrici has an almost indefinite power of growth, limited 
only by the cessation of the supply of nutrient material. In 
PL V, fig. 1, is drawn a specimen from the posterior portion 
of the perivisceral cavity of the earthworm,, which was found 
floating there with two others, being of unusually large size. 
One of the specimens was the -^-^^ih. of an inch in diameter, 
the contained vesicle of proportionate size, and the granules 
also much more conspicuous than is ordinarily the case. In 
the same worm the seminal vesicles and testicular sacs were 
found to be occupied by several individuals of Monocystis of 
enormous size, the whole of the cavities appeared to be filled 
by them, and the nourishment diverted to their use which 
should have been employed in the development of the seminal 
secretion. One of the largest of these Monocystes was ith 
of an inch in length, being of a linear form (fig. 2). When 
it is remembered that the ordinary length of a Monocystis 
Lumbrici is --^th of an inch or less, the strangeness of this 
large growth will be admitted. It appears that, when free to 
develop equally in all directions, the Gregarina assumes a 
more or less spheroidal form, as in the first instance, but that 
when growing in a confined space in company with other in- 
dividuals a linear increase is induced. 
The granules in the elongated form were much fewer than 
in the spheroidal one, and poured freely about in the interior. 
A considerable amount of activity was shown by this speci- 
men, and the tunic or enveloping membrane was thick, and 
occasionally showed striations, while in that from the peri- 
visceral cavity the membrane appeared much thinner and 
there was no movement. As a rule, it seems that the gra- 
nules are developed in the Gregarinse at the expense of the 
investing tunic, and that the larger the bulk of the granules 
the less is the activity of the Gregarina. 
Structure and function of the investing tunic. — I was in- 
duced some time since to believe, with Dr. Leidy, that the 
investing membrane of the Gregarinida is double, inasmuch 
as an appearance tending to prove that such was the case was 
witnessed both by him and myself in the Gregarina Blattce. I 
have now, however, reason to believe that the striations visible 
in the posterior sac of that species are produced merely by the 
contraction of a portion of the viscid material which fills it ; 
in fact, the investing membrane must merely be regarded as 
a dense layer of the same sarcodic material which forms the 
whole creature. The membrane which invests the whole 
Gregarina appears to be excessively thin and ill-defined, and 
more or less continuous with the viscid substance contained 
by it, which is denser nearer the exterior, and, in fact, seems 
