EYES OF THE SEROLID.E 359 



water by tlie character of the eyes. ' The results,' he says, 

 ' of my investigations into the minute structure of the eye 

 in Serolis may be briefly summed up as follows : — (1) The 

 shallow-water species invariably possess well-developed 

 eyes which are fundamentally similar to those of other 

 Isopocla, but differ in several particulars ; the retinula? are 

 composed of only four cells ; the rhabdom is often a highly 

 complicated structure unlike that of other Crustacea. 

 Another element unrepresented (?) in the eyes of other 

 Crustacea is present, consisting of two large hyaline nu- 

 cleated cells placed below the rhabdom and between the 

 retinal cells. (2) In the deep-sea species the eyes are 

 either altogether absent (Serolis antarctica), or, if present, 

 show signs of structural degeneration; no retinula, at 

 least nothing comparable to the retinula in the eyes of the 

 shallow-water species, is present, but the vitreous body is 

 represented. The vitreous bodies may be enclosed in a 

 sheath of pigment (Serolis necera), or there may be no 

 pigment present (Serolis gracilis^ Serolis Bromleyana).^ 



From examination of the contents of the stomachs 

 Mr. Beddard has come to the conclusion that these inter- 

 esting Crustaceans are upon occasion cannibals. 



Family 5. — Si^limromidce. 



The body is convex, the head transverse ; the pleon is 

 vaulted over the pleopods, its earlier segments, exclusive 

 or inclusive of the first, being usually fused into a shori 

 segment marked more or less by sutural lines, the terminal 

 segment being, on the other hand, very large. The eyes 

 are generally wide apart ; both pairs of antennse have the 

 flagellum multiarticulate and well marked off from the 

 peduncle. The mandibles have a three-jointed ' palp ; ' 

 the first maxillae have two plates, the second three ; the 

 maxillipeds are seven-jointed, the second joint being pro- 

 duced into a plate. The limbs of the perteon are sleuder, 

 generally with bifid fingers. The first three pairs of pleo- 

 pods are ciliated, with the outer branches not opercular ; 

 the second pair in the male have a stilet on the inner 



