1G4 THE VOYAGE OF H.M.S. CHALLENGER. 



which juts out as a lanceolate pointed projection, all the original spines affixed to this 

 part in the earlier stages having disappeared. The three outer spines on either side of 

 this projection arc still present in this stage, and the innermost of these spines is very 

 large and has already assumed the form characteristic of the subapical spines in the 

 adult animal, whereas the outermost is exceedingly small and easily recognised as 

 representing the posterior pair of dorsal spines in the adult animal. 



In the first post-larval stage, finally, the telson has assumed the precise appearance 

 characteristic of the adult animal, the middle of the exterior spines having been 

 wholly lost. 



Thus, of the spines occurring on the telson in the larva, three pairs only are 

 retained in the adult animal, viz., the lateral spines, which represent the anterior pair 

 of dorsal denticles, the outermost, on either side, of the terminal spines, constituting 

 the posterior pair of dorsal denticles, and the third spine on either side, counted from 

 the outer corner, which are modified to form the peculiar subapical spines of the adult 

 animal. All the other spines wholly disappear in the course of the larval development. 



The Uropoda (figs. 37-42). — As stated above, these limbs are entirely wanting in 

 the earliest larval stages (see fig. 36), not appearing till the last Calyptopis stage, when 

 they are (fig. 37) very small and have only an indistinct mark between the basal part 

 and the terminal plates, the latter being furnished with but very few bristles proceeding 

 from their apex ; of the plates, the exterior one is the longer, and has the outer corner 

 drawn out to a strong spine. In the following stages (figs. 38-40) the uropoda 

 develop by degrees more fully, the terminal plates increasing in length and becoming 

 furnished with a greater number of bristles, continued along their inner edge, till in the 

 first post-larval stage (fig. 42) they have almost attained the aspect characterising those 

 of the adult animal, though still somewhat shorter in relation to the telson. 



The Luminous Apparatus (figs. 9, 25-32). — Of the numerous organs constituting 

 this peculiar apparatus, those occurring in the eye-pedicles of the adult animal are first 

 developed. According to the statements of Metschnikoff", even in the Nauplius stage 

 the peculiar fascicle of glistening fibres, constituting the essential part of these organs, 

 is distinctly seen on either side of the larval eye, or ocellus, no trace of the compound 

 eyes being as yet observed. In all the succeeding stages these organs are readily 

 discerned, imbedded in the base of the developing eyes. The other organs, the true 

 luminous globules, make their appearance at a much later period, and are not all 

 developed at the same time, but appear successively. In the intermediate Furcilia 

 stage (PI. XXIX. fig. 6) only three such globules are developed, viz., the anterior of 

 the two pairs belonging to the trunk, and the foremost of the odd caudal globules. In 

 the last Furcilia stage the posterior pair Ijelonging to the trunk have likewise appeared, 

 though being still but very faintly defined (see fig. 29), as also another of the caudal 

 globules. The remaining two caudal globules successively ' appear in the following 



