LIFE HISTORIES OF THE PROTOZOA. 737 
muscular, and an inner, medullary or granular, layer, which are 
more distinct than in the Amæbæ, and also a nucleus. In form 
they are more or less worm-like. They are parasitic, living in 
many types of animals, especially the insects and worms, and’vary 
greatly in form. The largest species known is Gregarina gigantea 
(Fig. 131 after Van Beneden), which lives in the intestinal canal 
of the European lobster. It is worm-like, remarkably pearing be- 
ing -64 inch in length. It is, in fact, the largest one-celled animal 
known, and in size may be compared with the cells of some vege- 
tables; in the animal kingdom it is only surpassed by the eggs of 
birds, which are really cells. In this or ganism an external, struc- 
tureless, perfectly transparent membrane, with a double contour, 
can be very clearly distinguished. It represents the cell wall of 
other cells. Beneath this outer wall is a continuous layer of con- 
tractile substance, by which these animals retain their form, not 
changing as in the Ameba. It was first discovered in 1852, by 
Prof. J. Leidy. He showed that there existed under the cuticular, 
structureless membrane, a so-called muscular layer, which in con- 
tracting becomes longitudinally folded, so as to produce a marked 
striation. Van Beneden adds that in “the immense Gregarina of 
the lobster I have assured myself of the presence of, under the 
cuticle, a true system of muscular fibrillæ, comparable to those of 
the Infusoria.” From this fact he places these animals above the 
Amæbæ, which move by the simple contractility of their sarcode 
or protoplasm, a property of all animal and vegetable protoplasm 
generally. He therefore opposes the opinion of Heckel that the 
Gregarina is an Ameba, degraded by its parasitic life. 
The internal granular matter of the Gregarina is extremely 
mobile, like protoplasm generally. “The whole cavity of the 
body is filled,” says Van Beneden, “with a granular matter formed 
by a viscid liquid, which is perfectly transparent. This holds in 
Suspension fine granulations of a rounded form, which are formed 
by a highly refractive and slightly yellow matter.” In this gran- 
ular matter the nucleus is suspended. The nucleus is surrounded 
bya membrane, and the cavity of the vesicle is filled by a homo- 
_ 8eneous, colorless and transparent liquid. This nucleus contains 
an inner vesicle, or nucleolus, which has the singular feature of 
Ee hony appearing and disappearing in a very short space 
time. “If one of these Gregarine of moderate size is ob-— 
“ay the nucleus is seen at first provided with a single nucle- 
_ AMER. NATURALIST, VOL. VIII. T 
