10 



PEOF. M. M. HAETOG- ON THE 



with the interarthrodial membranes as long as the segments; 

 " plumes very long, olfactory lancet on 4th. 



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r 4th joint short annular, " 

 5th „ „ ; 



6th „ „ , 



7th „ obliquely truncated, annular, conical, longest on extero-dorsal side, overlapping 



8th, especially on outer side. 

 8th joint similar to 7th but longer, overlapping 9th segment. 

 9th ,, a narrow ring bearing on inner (anterior) edge an olfactory lancet. 

 10th „ almost bell-shaped, its produced distal margin overlapping the next on all sides, 

 especially ventrally and anteriorly ; 1 short plume. 

 These constitute the basal segment. 

 '11th joint short, cylindrical, expanding distally, convex postaxially, concave preaxially, 



bears on a projecting ridge atprcaxial flexor edge a plume and hook, serrated at base. 

 12th joint annular, bears on preaxial edge a plume, a hook serrated at base, and a short spiue. 

 13th „ annular, bears a short olfactory lancet, and a small slender hooked spine. 

 14th „ cylindrical, tapering distally, excavated on the preaxial side, distally for the 

 reception of the 15th segmeut, and bearing on its preaxial side a short process, which 

 gives off proximally and distally a strong spine, resembling together those vegetable 

 hairs known as " medifixi " or " malpighiaceous." 

 These constitute the first segment of the clasper. 

 15th joint an elongated sclerite, practically undeveloped on the postaxial side, strongly convex, 

 bulging out preaxially and, as it were, let in between the 14th and 16th segments (lying 

 chiefly in the former in flexion), and produced at each end into an apodeme. 

 16th joint elongated cylindrical-falciform, convex on its postaxial edge and bearing a long 

 plume ; preaxially bearing 2 stout " medifixed spines," a proximal and a distal, bearing 

 on the apex of the 15th and the base of the 17th joints respectively. 

 These form the second segment of the clasper. 

 17th joint elongated bluntly falciform, with a strong basal convexity on the preaxial side 

 underlying the spine of the 16th segment, and showing a slight indication of division 

 about its middle ; bearing on its postaxial side 6 plumes and a tuft of about 3 round its 

 apex, among these hairs one or two are pale*. This forms the last segment of the clasper. 



I 



Many segments have little angular processes both dorsally and ventrally near the post- 

 axial side, at their distal ends, articulating with corresponding notches on the adjoining 

 segments, and forming hinges limiting extension. Thus constituted, the male antennule 

 is a powerful clasper, formed of four consecutive pieces ; the basal extending to the 9th 

 and 10th joints, and having there a practically ball-and-socket motion, owing to the way 

 7 and 8 overlap 9, and 10 overlaps 11 ; the second piece extends from 11 to 14 inclusive, 

 and with the next piece forms the clasper proper ; 15 is simply a hinge by which 16 flexes 

 on 14, and 17 alone constitutes the last piece, flexing on 16 and lying on its dorsal surface. 

 All the joints flex in the same direction — preaxially. 



Proper Muscles. — 1. Basal group : (1) a long basal extensor originating in the outer part 

 of socket inserted on extensor edge of base of 4th joint ; (2) a short basal extensor origi- 

 nating on flexor side of base of 1st joint, crossing over and inserted with the former; 



* Claus describes the pale hairs as ending with a dark-coloured ring, like the hairs of the antennule of Daphnia. 

 In the specimen before me one is ringed at the apex, that of the fellow antennule is not. 



