134 MR. F. J. MEGGITT ON A 
is rough and ragged like that of the adult. Under it is a smooth 
homogeneous layer, ‘(0018-0029 mm. thick. Owing to the small 
size of the larva I have been unable to find any definite traces of 
muscles. Muscles must undoubtedly be present, however, for the 
larva is capable of sluggish contractions similar to those of the 
adult. 
The body within the cuticle is a nearly solid mass of paren- 
chyma. Just inside the cuticle the parenchyma forms a fairly 
compact sheath, but in proportion to its distance from the exterior 
it loses this compactness and becomes vacuolated, the centre itself 
being a fairly loose meshwork like that of the adult. The paren- 
chyma between the suckers is firmer than that elsewhere. The 
parenchyma itself is a faintly staining granular mass, forming a 
more or less definite meshwork through which dark-staining cells 
are scattered (Pl. IV. fig. 35). It is not probable that these are 
nuclei owing to their comparatively large size, °(003--005 mm. dia, ; 
inside them are often several darker staining bodies. In addition 
to these are smaller bodies like the former only smaller, ‘0016-— 
-0025 mm.; they are also present in young suckers, and may 
possibly be nuclei. Occasionally circular granular bodies, 
‘004 mm. dia., not so deeply staining as the others, are to be 
seen. These I take to be the refractive granules (calcareous 
bodies) apparently present on the surface of the larva. Running 
in all directions through the parenchyma are delicate fibres, 
which may possibly be the rudiments of muscles. It is ex- 
ceedingly ditticult to state the histological significance of all 
these different structures owing to their small size and general 
indefiniteness. 
At the posterior end of the larva is a small depression running 
-016 mm. into the body, its apex expanding into an oval chamber, 
with its long axis parallel to that of the larva (PI. IV. fig. 36). 
On all sides but one, this invagination is enclosed by the body, 
but on the fourth side it appears to be open to the exterior; if 
seen from this side, it shows the entire depression—in shape like 
the gullet and buccal groove of Parameaciwm—which is not 
visible from the other side (Pl. IV. figs. 39, 40). The cuticle 
covers its exterior, so that it is a true invagination. Presumably 
this corresponds to the heart-shaped bubble in which, according 
to Kraemer, the longitudinal excretory canals open. I have been 
unable to see any signs of excretory organs, however. 
There are no traces of reproductive organs in such a young 
stage. 
The presence of the larva is fatal to the Cyclops, apparently 
causing its starvation. The orange globules usually present in 
the head of the Cyclops vanish, and the ovary degenerates and 
dwindles to half its usual size. The activity of the Cyclops 
also suffers ; it does not swim so rapidly and takes much more 
frequent and longer rests than its fellows. Ultimately it dies. 
This sluggishness and death would be favourable to the larva, for 
