48 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 l. Draw a large outline of the dorsal aspect of a cope- 

 pod, not putting in any appendages except the antennae. 

 Represent accurately the sense-hairs on the antennae and 

 the abdominal bristles. Number the thoracic and abdomi- 

 nal segments and carefully label all the parts. 



Study the appendages. The thoracic appendages are all 

 biramous, but bear no gills ; the last pair may be rudimentary. 

 The cephalic appendages consist of two pairs of antennae, one 

 pair of mandibles, and two pairs of maxillae, 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 hairg. 



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 fsecal 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 



