202 DR. M‘INTOSH, ON THE CARCINUS M@NAS. 
heart, is free from theirinroads. A series of specimens shows 
them in the muscles of the stomach, those in the neighbour- 
hood of the heart, and in the generative organs. Injection 
of the arteries with vermilion brings out those attached to 
them with great clearness. Season does not seem to affect 
their presence, structure, and stage of development. On the 
whole, they are most numerous in males. 
On placing an egg under the pressure of a thin glass cover, 
and magnifying 180 diam., the aspect isas shown in Pl. VIII, 
figs. 1 and 2. The egg-case (fig. 4) is very tough, and 
apparently consists of two layers marked by minute striz 
and specks; but the outer cannot always be seen, and is 
probably due to a delicate investment derived from the sur- 
rounding tissues. The contained living embryo differs little 
in apparent age and development in the various crabs. The 
parasite has a gentle gliding movement in the egg, and, when 
at rest, is susceptible of stimulation; for it becomes active 
when slight and intermittent pressure is applied, or when the 
effects of evaporation are felt. They will live for sixteen 
hours or more after immersion in weak spirit. The margin 
of the embryo im situ is observed to be finely crenate for 
about half the circumference. It lies in a doubled or coiled 
position, as in fig. 1, where the embryo is seen in profile. A 
front view is given in fig. 2. On pressing with force on the 
egg, so as to cause it to burst, it is found that the embryo 
generally emerges with the broad end containing the large 
cells first, and sometimes the small end clings firmly to the 
interior of the capsule, from the fact, afterwards to be 
explained, of its being plentifully suppled with minute 
recurved spikes. This is easily illustrated by placing some 
ova in fresh water for a few days, and allowing the egg- 
capsules to burst. 
Fig. 3 represents various views of the embryo under the 
high power of a dissecting lens. A single individual, magnified 
180 diameters, is shown in fig. 5. It crawls about after 
extrusion with an undulating motion, like a Planaria, altering 
the outline of its body at pleasure, and throwing it into 
wrinkles; but the lower end in this figure generally remains 
largest. At the upper or small end is observed a circular 
oral sucker (f, fig. 5) from which an cesophagus proceeds 
downwards, dilating after a short progress into an ovoid 
sac (yg) (? if the homologue of the pharyngeal bulb of a 
Cercarian), and, again contracting to its original size, passes 
down the middle of the body, gradually widening as it 
approaches the larger end of the animal, and dividing into 
two wide ducts (alimentary czeca), which fork outwards to the 
