SECT, xv CLASSIFICATION OF CRUSTACEA 265 



the limbs. In consequence, however, of our method of 

 deducing the limbs from the Annelidan parapodia we 

 do not ourselves experience this difficulty. The typical 

 Phyllopodan limb is, according to our view, composed 

 of the dorsal parapodium carrying on the dorsal side 

 the gill and the sensory cirrus, and on the ventral side 

 a row of sensory endites, with the remains of the 

 ventral parapodium as masticatory ridge. The parts 

 of these limbs which would be useless to the Copepod 

 would naturally degenerate, i.e. I, the gills, because the 

 animal breathes through its integument ; 2, the sensory 

 endites, because the animal would no longer require 

 to use its limbs in the way Apus uses them to rake 

 together prey into the ventral middle-line ; and 3, con- 

 sequently also the masticatory ridge which in Apus 

 forwards food thus raked together towards the mouth. 

 On the degeneration of these parts we have left only 

 the dorsal parapodium with the sensory cirrus, i.e. the 

 endo- and exopodite of the typical Copepod Ihnb. 



Grenacher's account of the unpaired " eye " of 

 Calanella differs somewhat from that of Apus ; 

 although there can be little doubt that the two are 

 homologous. In Calanella only three "retinae" arc 

 developed, each consisting of comparatively few 

 retinal cells. There is no trace of crystal cones 

 or rhabdomeres, and the pigment is in the centre 

 of the group. The nerves from the retinal cells 

 come from their inner ends, their sensory ends 

 pointing outwards. A comparative study of these 

 unpaired " eyes " has long been a desideratum. 



We thus suggest the deduction of the Copepoda 



