196 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



poda. There is an incomplete articulation near the 

 middle. At the apex of the abdomen there are two short 

 papillae known as the furca or caudal stylets, which 

 usually have four or five plumose hairs on their posterior 

 margins. 



There are twelve pairs of appendages* (Plate II., fig. 1) 

 as follows : — One pair of antennules, one pair of antennae, 

 one pair of mandibles, two pairs of maxilla?, two pairs of 

 maxillipedes, and five pairs of feet, the first three pairs of 

 feet only being adapted for swimming. 



The eyes appear as a reddish spot in the living animal, 

 and are situated on the dorsal surface mid-way between 

 the frontal margin and the transverse line of the cephalo- 

 thorax. When this spot is examined microscopically 

 (Plate III., fig. 13) it is found to consist of two lateral 

 eyes closely approximated, embedded in a mass of reddish- 

 black pigment, and wholly under the carapace. Each eye 

 has a simple, spherical, crystalline lens, beneath a thin 

 cornea. Behind the lens is a row of retinal cells of fairly 

 large size, lined internally with a tapetum or pigment 

 layer. A chitin division lined with deep red pigment 

 separates the two eyes. The earlier Zoologists had con- 

 siderable doubt as to the true position of the eyes, some 

 even believed the animals were blind. -Others 

 mistook the semi-circular suckers on the frontal margin 

 of Caligus already referred to for the organs of vision, 

 giving them the name " Binoculus." 



The antennules are placed at the external margin, just 

 behind the suture on the frontal plate, and each consists 

 of two joints. The basal joint is much larger than the 

 apical, and is. clothed on its upper margin with plumose 

 setae. 



* The minute details of the jointing and setse of the appendages are not 

 shown in these figures. 



