118 THE VOYAGE OF H.M.S. CHALLENGEE. 



(see figs. 15-18) are comparatively simple in structure, and perfectly similar in appear- 

 ance, occurring as single stems expanded at the extremity into two short diverging 

 corners, and having along the hinder edge a regular series of digitiform gill-lobules, 

 diminishing in length towards each extremity. The last pair (fig. 19), on the other hand, 

 are very large and complex, divided as usual into two principal portions pointing in 

 opposite directions, the posterior of which is the larger, and provided with several curved 

 secondary branches, each having along one of its edges a regular series of gill-lobules. 

 Thepleopodaof the female (fig. 21) do not exhibit any essential peculiarities of structure. 

 The copulatory appendages to the two first pairs of pleopoda in the male (see PI. XXI. 

 figs. 6,7) are, on the whole, not so fully developed as in most other EuphausiidiB. Those 

 on the first pair (fig. 6) form a somewhat curved lamella, doubling over the inner 

 plate of the pleopod, and with the inner edge finely serrate. From this lamella, also, 

 proceed two comparatively smaU processes, the outer of which is mucroniform and highly 

 chitinised, whereas the inner is narrow linguiform, and quite soft. Moreover, a slender 

 incurved spine is seen to spring from a rounded prominence on the outer margin. The 

 appendages of the second pair of pleopoda (fig. 7) constitute merely a slight two-lobed 

 expansion of the inner edge of the principal plate. 



The telson (see PI. XX. fig. 22) exhibits the usual slender form, tapering gradually 

 toward the apex, which is but slightly produced and bluntly lanceolate (see fig. 2,3). The 

 subapical spines are of moderate length and perfectly smooth. Moreover, two pairs of 

 small denticles occur on the dorsal face of the telson. 



The uropoda (see fig. 22) have the inner plate very narrow and a trifle longer than 

 the outer, reaching, when extended posteriorly, to the tip of the telson. The outer plate 

 of each is rather broader, and truncate at the apex, with the outer corner projecting as an 

 acute angle. 



Of the female specimens in the collection, two are ovigerous, a condition very rarel}- 

 met with among preserved specimens of Euphausiidse. The eggs were deposited in two 

 well-defined ovisacs (see PI. XX. figs. 1, 2) placed side by side beneath the posterior 

 part of the trunk. These .ovisacs do not consist of incubatory lamellas, as in other 

 Schizopoda, but merely of an exceedingly thin membrane, derived, it would seem, from 

 some glutinous fluid issuing along with the ova and coagulated by the action of the sea- 

 water as a delicate envelope surrounding and keeping the ova together during the 

 embryonal development. In form, the ovisacs are somewhat conical, being broadest 

 posteriorly and gradually tapering forward, where they are connate with the inner half of 

 the ischial joint of the antepenultimate pair of legs, covering too, exteriorly, a 

 considerable part of the succeeding pair. This peculiar arrangement of the ovisacs fullj^ 

 suffices, it would seem, to account for a striking anomaly met with in the present species 

 and mentioned above, viz., the total absence of exojDods on the posterior pairs of legs in 

 the females. It is, indeed, evident that these organs would be quite inoperative, and 



