48 ZOOLOGICAL EXERCISES. 
13. Seemental organs.—Cut out one of the convoluted 
segmental organs from a segment behind the repro- 
ductive system, and examine with the microscope. 
Notice its expanded and ciliated extremity; the 
transparent portion doubled upon, and closely con- 
nected with, a darker portion which is surrounded by 
granular cells. 
14. Nervous system.—Observe the ventral nerve cord, 
swelling slightly in each segment, but not markedly 
ganglated. ‘Trace it up anteriorly, catting when 
necessary with the knife, until it is seen to divide 
into two branches which pass round the alimentary 
canal, and meet to form the double ganglion on the 
pharynx which was previously seen (8). Cut out a 
portion and examine with the inch objective. It 
will be seen to give off two pairs of nerves from 
each swollen portion, or ganglion, and a single pair 
from the narrower portion. Notice that the narrower 
portion is double. Examine with the highest power. 
Try to make out the longitudinal rows of tubular 
fibres on the upper side of the cord. 
15. Muscular system.—Cut out a transverse piece of the 
integument and sub-cutaneous muscular layer from 
the ventral portion, containing a pair of sete from 
each of the ventral rows, and place it on a slide, in 
water, with the exterior surface upward. Examine 
with the quarter objective. Observe the S shaped 
sete ; the cellular dermis; and, lying below it, the 
muscular layer. Notice that it is made up of two 
sets of fibres at right angles to each other. Satisty 
yourself by focussing up and down, that in the upper 
(i.e. the outer) layer the fibres are transverse to the 
axis of the body ; while in the lower (ie. the inner) 
