THE COPEPODA 95 



appendages afterwards appearing, it is believed that they represent 

 the antennae and mandibles of the nauplius. The organs of the 

 adult are gradually differentiated within the cuticular sac, which 

 enlarges with the growth of the animal. The pointed posterior 

 end of the sac is surrounded by rows of recurved hooks (D), and 

 these appear to be used in boring a way out through the tissues 

 of the host when development is complete (E). The reproductive 

 organs are developed before the parasites escape from the host. 

 After escaping, a single moult takes place and sexual maturity 

 is reached. 



The life-history of the Monstrillidae may be compared with that 

 of the male Enterognathus described above, in which the earlier 

 larval stages and the adult are free-swimming, while the intervening 

 stages are parasitic and degenerate, and in which also the adult is 

 incapable of feeding. 



MORPHOLOGY OF BRANCHIURA. 



The body is much flattened, and is divided into three regions, 

 an unsegmented, cephalothoracic region followed by three free 

 thoracic somites and an unsegmented abdomen (Fig. 54). The 

 cephalothoracic region is covered by a greatly developed head-shield 

 or carapace, which, while not projecting beyond the articulation of 

 the succeeding somite as a distinct " shell-fold," is expanded on each 

 side in a great wing-like pleural fold. In many species the lateral 

 folds are produced backwards and cover the thoracic somites and 

 their appendages, and sometimes even the abdomen. The abdomen 

 is notched or bilobed, and bears a pair of minute furcal rami (/). 



Appendages. The antennules are small, consisting of four 

 segments, of which the first is divided into two parts and is 

 provided with a large hooked claw and some smaller spines, used 

 for attachment to the host. The antennae are also short, unirumous 

 in the adult, of four segments, the basal part provided with stout 

 spines. 



The mouth-parts are suctorial, the upper and lower lips together 

 forming a proboscis (Fig. 54, p) within which are enclosed the 

 mandibles and maxillulae. The maxillulae are never included in 

 the proboscis in suctorial Eucopepoda. 



The mandibles are without palps in the adult and have sickle- 

 shaped, serrated tips. The maxillulae are stated to be wanting in 

 the genus Dolops. In Argulus they are simple, lancet-like blades. 

 The maxillae (" first maxillipeds ") are very remarkably modified. 

 Except in the genus Dolops, where they end in stout hooked claws, 

 they are represented chiefly by a pair of large adhesive suckers 

 (Fig. 54, mx"), situated some distance in front of the proboscis. The 

 sucker is developed from the basal portion of the appendage, the 



