18 PEOF. M. M. HAETOG ON THE 



inwards and downwards to enter the endopodite and runs along its outer side to the hasal 

 angle of the 2nd joint; this must abduct, but probably aho flexes the joint. 



Muscles of Exopodite. — A double slip rises from the outer angle of the base of the 

 ramus and is inserted into the inner basal angles of the 2nd and 3rd joints of the 

 exopodite, which it adducts and probably flexes. 



Extrinsic Muscles of Oar-feet. — Sets converging like a fan from their insertions on 

 the sides and top of the tergum of the segment to be inserted at the base of the coxo- 

 podite, the posterior or flexor sets being inserted into the apodeme referred to above. 

 The motion of the limbs as oars may now be understood ; starting from extension, they 

 are inclined slightly forward at an angle of about 70° to the body. Then, in flexion, 

 they are drawn rapidly back so as to lie almost horizontally against the body ; at the same 

 time by abduction of the basipodite the limbs of the pair are drawn away from the 

 middle line, while the proper abductor of the exopodite draws it again away from the 

 inner ramus, so that the grasp of the limb on the water is at its fullest, owing to the 

 fringes of plumes and saws. In extreme flexion the limb is further drawn back on the 

 outer side, where its socket is, as it were, too big for it, thus producing the sliding-seat 

 effect mentioned above. 



Then the limb is extended ; during this the flexors of the rami come into play so as to 

 keep them bent with their axes parallel to the body, and at the same time their adductors 

 come into play, rotating the limb and its rami, which now have their outer edges (fringed 

 with saws and not with plumes) turned forwards, w r hile their inturned adducted apices 

 meet on the middle line ; thus there is a decided feathering. In extreme extension 

 a slight abduction takes place and the rami straighten, presumably by the spring action 

 of their joints, as I have noticed in my dissections that the joints of the rami are 

 always extended *. 



X. Rudimentary Feet, 1st pair (5th Thoracic)^ (PI. II. figs. 4, 5, 6), at the extreme sides 

 of the ventral surface,but still not at all lateral. Basal joint squarish, prolonged at outer 

 angle into a process bearing a long plume ; bevelled at inner angle to bear the distal joint. 

 Distal joint elongated, cylindrical, about as long as basal joint, bearing on inner edge a 

 sharp tooth % and tipped by a long plume. 



Muscles, an extensor and a flexor attached to the sides of the tergum of its segment. 



XL Rudimentary Feet, 2nd pair (6th Thoracic). Differing slightly in the two sexes; 

 in both reduced to an elliptical flap overlying the sexual aperture and forming a valve, 

 with its distal edge close against the boundary of the next segment. 



Female. Best seen in profile position ; forms a transverse oval flap stretching one third 

 of the width of animal from ventral edge ; bears towards outer lower angle two teeth 

 and a short plume. 



Male. Distinctly ventral and approximated, almost united along their anterior edge, 



* From Giesbrecht's beautiful figures it "would appear that the musculature I have described is typical in the 

 Copcpoda ; he gives, however, no description of what he has so carefully drawn. 



t In this genus specific characters of great constancy are to be got from this limb. 



% I once found, as a monstrosity, this tooth prolonged into a short serrated spine — an approach to its condition in 

 C. serrulatus. 



