SEA-FISHERIES LABORATORY. 228 



verse section. It is composed of five distinct parts — an 

 oval cephalo-thorax, three thoracic, and one terminal 

 segment, representing the genital segment and abdomen. 

 The anterior portion of the genital segment in the female 

 is indistinctty divided into eleven joints. 



The cephalo-thorax attains its greatest width just 

 behind the eyes ; beyond that point the sides converge 

 until they reach the first thoracic segment. The cephalo- 

 thorax is produced anteriorly into a broad blunt rostrum. 

 In the very early cyclops stage (Plate IV., fig. 3), the 

 rostrum is further produced into a short triangular 

 filament which secures the parasite to its host. 

 The eyes (Plate V., fig. 3) are situated on the dorsal 

 surface a short distance behind the rostrum. In the 

 living animal they appear as a dark red spot with a 

 crystalline lens projecting slightly at each side. When 

 examined microscopically the structure is found to be the 

 same as that described in Lepeophtheirus. A thin cornea 

 encloses a spherical crystalline lens. Behind the lens a 

 row of fairly large retinal cells is lined internally with a 

 tapetum layer. A chitinous septum lined with deep red 

 pigment separates the two eyes. The appendages attached 

 to the cephalo-thorax are as follows : — 



The antennules are placed at the posterior angles of the 

 lateral margins of the rostrum. They are short, and are 

 composed of four nearly equal joints furnished with fine 

 setse. 



The antennae are composed of two joints. The apical 

 joint is provided with a strong claw on its external angle. 

 The antennae usually project beyond the rostrum, and it 

 is by means of these that the attachment to the host is 

 maintained when the filament is broken off. 



The mandibles are not enclosed in the suctorial mouth. 

 They are situated at the base of the lateral surfaces of the 





