MOKPHOLOGY OP CYCLOPS. 9 



I. Antennule or first antenna* (PL I. figs. 1, 2).— This is differently formed in the 

 two sexes, in both acting as a strong oar, but in the male acting also as a clasper and 

 correspondingly complicated. In the female the preaxial edge is convex to the extensor 

 edge, while the reverse holds for the male. Chiefly on the preaxial and ventral edges 

 in both are borne hairs and spines, partly olfactory in function, partly plumes in- 

 creasing the swimming-surface. There are 17 segments in both sexes of this species, 

 and its total length in the female is about as long as the cephalothorax and first thoracic 

 segment, but may not extend beyond the carapace. 



Female (PI. I. fig. 1). — 1st joint obloug falciform, 5 preaxial, 3 ventral plumes. 

 2nd annular, 2 preaxial, 2 ventral plumes. 

 3rd annular shorter, 1 preaxial, ] ventral plume. 

 ■4th shortly cylindrical, 4 preaxial, 2 ventral plumes. 



5th smaller in all dimensions, shortly cylindrical, 2 preaxial pi. and 1 hair, 1 dorsal plume. 

 6th annular, 1 preaxial plume, 1 hair. 

 7th cylindrical, 1 prcax. olf. hair, 1 ventral plume. 



8th and 9th annular, conical (distal ends expanded), each with 1 preaxial plume. 

 10th broadly annular, 1 preaxial plume. 

 11th broadly annular, no plume. 



12th truncate, conical, dilated distally, 1 preaxial plume, 1 olfactory lancet. 

 13th shortly cylindrical, no plumes. 

 14th „ „ 1 ventral plume. 



15th cylindrical, conical, dilated distally, 1 preaxial, 1 postaxial plume. 

 16th „ „ „ 2 preaxial, 1 postaxial plumes. 



17th, elongated cylindrical, slightly dilated distally, ending in an obtuse knob, 1 post- 

 axial plume halfway up, and a wreath round apex of 5 plumes, a (preaxial) pale hair, 

 a hooked hair, and an olfactory (with a dark-bordered shaft and a long taper apex). 



The following table gives the relative lengths of the separate segments of the female 

 antennule: — 



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 

 25 4 3 11 8 4 10 4 4 5 6 7 5 6 9 11 14 



The proper muscles are as follows : — Extensors. (1) Short extensors : a group of three arising together 

 on the preaxial side of the basal joint ; the most proximal and postaxial inserted at the base of the 2nd 

 joint; the next with a partial insertion at the base of the 2nd, u ud a full insertion at the base of the 5th, 

 the third, most preaxial, running with intersections or partial insertions with the two former to its proper 

 insertion in the base of the 8th joint. (2) Long extensor : origin behind the former; insertion into base 

 of 17th joint. Flexor : a muscular slip running from postaxial side of 1st to base of last joint. 



Male (PI. I. fig. 2). — Divided into 3 distinct folding segments by special joints so as to serve as 

 clasper, and jointed by a ball-and-socket with a basal segment; these will be noticed 

 after detailed consideration of the joints. 



1st joint elongated, constricted at base, convex on anterior surface, which bears 4 short 

 plumes and 2 long ones ; lateral face with three olfactory lancets (the 3rd " lancet " 

 with one of the long plumes is really on the distal arthrodial membrane). 



2nd joint shortly cylindrical, 2 short plumes. 



3rd „ short, annular, 1 long and 1 short plume (att. of basal extensors). 



* A consideration of the morphology of these and the next pair of appendages is deferred to the section on the 

 nervous system. 



SECOND SERIES. — ZOOLOGY, VOL. V. 2 



