COPEPODA 335 



necessarily accompanied by a high degree of degeneration. The life 

 histories of parasites are often complicated, and may involve re- 

 markable changes of habit. Degenerate forms usually reach one of the 

 Cyclops stages and may pass through them all before they begin to 

 degrade. Often the male is less degenerate than the female : he may be 

 free-swimming while she is sedentary, or may be much smaller and 

 cling to her body. It is only possible here to mention a few of the 

 numerous genera of these interesting parasites. 



NotodelphySy commensal in the pharynx of ascidians, is clumsy 

 bodied, and has a large dorsal tgg pouch on the 5th and 6th thoracic 

 somites, but can swim and is sometimes captured outside the host. 



Monstrilla has a very remarkable life history. The adults of both 

 sexes are free-swimming, as are the newly-hatched Nauplii, but the 

 intermediate stages are parasitic in various polychaets, where they 



ex. 



Fig. 240. The maxilla of Calanus. ex. small prominence which perhaps re 

 presents the exopodite ; i and 2, endites representing the first two segments 

 9, terminal segment. 



9, terminal segment 



absorb nourishment by means of a pair of long, flexible processes 

 which represent the antennae. In this stage they lay up a food supply 

 for the entire life cycle, throughout which the animals are without 

 functional mouth parts or alimentary canal. 



Chondracanthus (Fig. 241), which infests the gills of various marine 

 fishes, has in the adult stage a large female, whose body is produced 

 into irregular, paired lobes and her appendages vestigial, though the 

 mouth has not a proboscis. The males are small, retain more of the 

 copepod organization than the female, and cling by hook-like 

 antennae to her body. 



Caligus, ectoparasitic, mainly in the gill chambers of fishes, is 

 clumsily built and has a suctorial proboscis, but retains the power of 

 swimming. Its sexes do not differ greatly. 



Lernaea (Fig. 242) hatches as a Nauplius and at the first Cyclops 



