l7itrodiictto?i to Ajiimal Morphology. 347 



hinder the mandible and maxillipede. The post ab- 

 domen bears a fringe of bristles, and often is split into 

 rudder-like processes ; many are acardiac. 



Two orders are included : — 



I. Gnathostomata — free, minute, marine, or freshwater, 

 with developed jaws, and a moderate post-abdomen. This 

 includes two families: — i. Cyclopidae — first pair of anten- 

 nae long, oar-like, with (on the right only, Diaptomus) 

 thickened clasping joints in the male ; the female carries 

 two (one in Diaptomus and Canthocamptus) lateral egg- 

 sacs ; eye either median (Cyclops, Diaptomus) or paired 

 (Cetochilus, Sapphirina). The male Sapphirina is luminous. 

 Cetochilus sometimes dyes the sea a deep red. Monstrilla, 

 Calanus Pontella, and Corycaea are often made types of sub- 

 families. 2. Notodelphidae — parasites in the branchial sacs 

 ofAscidians; bodyii-12 ringed; in the females the fourth 

 and fifth metameres are united, forming a brood-sac for the 

 eggs ; maxillae many-cleft ; first abdominal ring joined to the 

 cephalothorax. 



Order 2. Siphonostomata Fig. 39. 



(Zc/r^///^)— adults ecto-para- 

 sitic on fish, with suctorial 

 mouths, soft bodies, and 

 retrogressive metamorphosis ; 

 jaws reduced to bristles ; thorax 

 imperfectly or not segmented ; 

 front feet hook- or sucker-like ; 

 the males are often pigmy, and 

 the females usually carry their 



eggs, like Cyclops, in two Cyclop quadricomis, with its two 



f-i-11 • 1 J iU r„i egg sacs. Nauplius larva. 



sacs. They include the fol- 

 lowing families : — i. Ergasilidse — passage forms, the females 

 only parasitic ; body thick ; antennae jointed and bristled ; 

 second pair clawed ; post-abdomen jointed, with bristle-bear- 

 ing tail ; abdominal feet removed from the medial line ; the 

 males in Nicothoe, &c., are Cyclops-like, and in the female 

 (a lobster parasite) the abdomen forms on each side a long 

 lateral sac, and the &g% clusters are between these. The 



