A COPEPOD 59 
by the rhythmic contractions of the intestine. Other copepods 
possess a dorsal heart. There are no special respiratory organs. 
How is respiration carried on? The excretory system consists 
of a pair of coiled tubes, called the shell glands, which lie in the 
forward part of the cephalothorax and have external openings 
near the base of the first pair of thoracic appendages. 
The reproductive system consists of median or paired organs in 
the dorsal portion of the cephalothorax above the intestine. In 
the female the ovaries are often conspicuous as a pair of large 
branched organs. The oviducts are paired and lead to the exter- 
nal sexual openings in the first abdominal segment. Appended 
to the first abdominal segment may be a pair of egg-sacs contain- 
ing fertilized eggs which are cemented together by means of a 
secretion of the oviduct. In the male the reproductive gland is 
the median testis, which communicates by means of paired vasa 
deferentia with the external sexual openings, which are also in 
the first abdominal segment. The spermatozoa collect in the 
terminal portion of each vas deferens and form there a small 
mass known as a spermatophore. The two spermatophores, during 
the act of pairing, pass to the female and fertilize the ova. The 
male animals are much less numerous than the females. 
The reproductive glands of the copepod can be observed as 
above described only during times of sexual activity. At other 
times they can be seen only in part or not at all. 
The muscular system can be easily seen to consist of striated 
muscle fibers. Longitudinal as well as converging fibers will 
be seen at each appendage. . 
The nervous system may be seen in favorable specimens as a 
ventral strand in the cephalothorax connecting with the large 
dorsal brain. 
Exercise 4. Draw a side view of the animal, showing as many of 
the internal organs as you have observed. 
