54 INVERTEBRATE ZOOLOGY 
to form clasping organs, by which the female is held during 
pairing. In Cyclops, which is the commonest freshwater genus 
of the Copepoda, the first thoracic somite is fused with the 
head, leaving only four free thoracic somites. The abdomen 
bears no appendages. In the female the first two abdominal 
somites may be fused together. 
Exercise 1. Draw a large outline of the dorsal aspect of a cope- 
pod, not putting in any appendages except the antenna. 
Represent accurately the sense-hairs on the antenne and 
the caudal bristles. Number the thoracic and abdominal 
segments and carefully label all the parts. 
Study the appendages. The thoracic appendages are bira- 
mous. They do not bear gills, and the fifth pair is rudimentary. 
The cephalic appendages consist of two pairs of antennae, one 
pair of mandibles, and two pairs of maxille, the second pair of 
which are without protopodites. The exopodites and endopo- 
dites of this second pair join the body separately in conse- 
quence and may appear as independent appendages. 
Exercise 2. Draw a side view of an animal showing the append- 
ages in position. 
Exercise 3. Draw an outline of a thoracic leg on a large scale, 
showing accurately all the joints and hairs. 
Compare the copepod with the young larva of the crab or the 
lobster. Enumerate the points of structural similarity between 
them. 
Internal anatomy. This can be best studied in the live animal. 
The alimentary tract is straight and of large diameter, and often 
contains dark-colored feecal matter. The mouth has a ventral 
position, as in other crustaceans, while the anus is dorsal. There 
is no liver or other accessory glandular organ. The circulatory 
system in Cyclops consists of the colorless blood fluid alone, 
there being no heart. The blood is, however, kept in circulation 
