THE SHORE CRAB. raf 
which proceeds a longer longitudinal piece which is 
ridged or crenulated. | 
8, Wash out the body of the crab with a camel-hair brush, 
and examine the reproductive organs. Trace down 
as far as you ‘can the efferent ducts; in the female 
towards the centre of the sternum; in the male 
towards the bases of the last pair of legs. Hxamine 
a, portion of the sex gland with the microscope. The 
ova are of the usual form. The spermatozoa are 
radiating cells, with the head in the centre. They 
have no movements. 
9, Wash out the body again and cover with clean water. 
Examine the nervous system, Notice the large 
round thoracic ganglion lying in the middle of the 
thorax, and sending off radiating nerve cords to the 
legs, &c. Anteriorly are the two cesophageal cords 
which unite the thoracic to the cerebral ganglion, 
already seen. ~ Posteriorly a single non-gangliated 
cord passes into the abdomen. Remove the thoracic 
ganglion with some of the cords, and examine with 
your highest power. 
10, Examine the branchiw. There are either seven 
(catometopa), or nine (cyclometopa), on each side. 
Above them lies longitudinally a long flagellum, 
pointing backward, which serves by its movements 
to keep the branchiz clean. Cut them away and 
observe that they are attached to the appendages. 
Examine a portion of one with the microscope. They 
are not ciliated. 
11. Cut off a small portion of one of the muscles of the 
legs, and tease it out with needles in a drop of water 
on a slide. Examine with the quarter objective. It 
is composed of fibres transversely striated. 
