COPEPODA. 



397 



E.V 



the fifth pair is much reduced (Cyclops) or absent. In many 

 Calanidae though absent in the female, it is in the male modified, 

 unsymmetrically, as a pair of copulatory organs. 



It will be noticed that when five pairs of swimming feet are 

 present, the number of the appendages corresponds with that 

 found in the Cirripedes. , 



The nervous System consists in the 

 Calanidae of a supra- oesophageal gan- 

 glion, supplying the eyes and anterior 

 antennae, a circumoesophageal ring giving 

 off nerves to the second antennae, and a 

 chain of seven or fewer median ganglia be- 

 hind the oesophagus, of which the two 

 anterior supply the mandibles, maxillae 

 and maxillipeds. In the Corycaeidae 

 however and in the parasitic forms the 

 ganglia are concentrated into a ring 

 round the oesophagus from which a single 

 or double cord, in which ganglion cells are 

 present, is continued backwards. 



Sense organs. A median frontal eye (nauplius or Cyclops 

 eye) is present (Figs. 257 and 260), though lost in the later 

 stages of parasitic forms. It is divided into three parts, 

 paired dorsal and median ventral, and the former are provided 

 with cuticular lenses. In the pelagic Pontellidae the median 

 eye is highly developed and provided with deep and cuticular 

 lenses. The lateral divisions of it are also largely developed 

 in the Corycaeidae. In the Branchiura alone among the 

 Copepoda compound lateral eyes are present (Fig. 267) in 

 addition to the median eye. 



Delicate olfactory hairs and rods are present on the anterior 

 antennae, principally in the male (Fig. 258). 



Phosphorescent organs. Some pelagic Copepods (some Pontel- 

 lidae and Oncaea) emit bright sparkles of greenish or bluish 

 light, produced by the contact of the secretion of skin-glands 

 with the water. These are present also in the larvae, and the 

 arrangement of the glands and the colour of the light is charac- 

 teristic of the species.* 



FIG. 261. A swimming foot 

 of Cyclops. En endopo- 

 dite ; Ex exopodite. 



* Giesbrecht, Mitth. lib. Copepoden 8. Ueb. d. Leuchten d. pelagischen 

 Copepoden, Naples, Mitth., Bd. 11, p. 648 (1895). 



