158 THE VOYAGE OF H.M.S, CHALLENGEE. 



preceding stages, sideways. Of the two branches, the one has assumed the character of 

 the scale, the other of the flagellum. Both flagella of the antennulaj have become 

 considerably elongated and divided into distinct articulations. The two anterior pairs 

 of legs are more fully developed and nearly equal in size, both having acquired 

 the geniculate bend characteristic of the adult animal. Posterior to these, another pair 

 of legs have developed, and the gills are distinctly visible, though still exhibiting a 

 very simple structure. The hindmost pair of luminous globules on the trunk have 

 just appeared, and on the tail all the globules are quite distinct. Length of body 

 3-80 mm. 



Last Cyrtopia Stage (fig. 9). — In this stage the flagellum of the antennge has 

 increased considerably in length, and its basal part is clearly defined from the terminal 

 part. On the trunk occur three pairs of distinctly developed, geniculate legs, and 

 behind them another much smaller pair have made their appearance. The endopodite 

 of the maxillijjeds is somewhat prolonged, and has a more pronounced pediform appear- 

 ance. Finally, the gills are somewhat more complex in structure than in the preceding 

 stages. Length 4" 15 mm. 



First Post- Larval Stage (fig. 10). — The full number of legs is now developed, and the 

 animal, on the whole, exhiljits all the characters distinguishing the adult form, except that 

 the flageUa of the antennulse and antennae have not yet attained their full length, that 

 the gills are still comparatively simple in structure, and, finally, that the anterior pair of 

 the lateral denticles of the carapace are not yet developed. Length of the animal in 

 •this stage about 5 mm. 



B. Development of the several Appendages of the Body (PI. XXX.). 



The Comp)ound Eyes (fig. 9). — In the Nauplius and Metanauplius stages these 

 organs are entirely wanting, as shown to be the case in the last of these stages in 

 Nyctiphanes. In the Calyptopis stages they are still very imperfectly developed, 

 forming immobile rounded masses, wholly covered by the carapace and devoid of anj- 

 distinctiy developed visual elements. In the last only of these stages a faint trace of the 

 ocular pigment and a few radiating stripes may be seen in the anterior part of the eyes. 

 Not till the Furcilia stages do the organs (fig. 9) become mobile and pedunculate, as also 

 freely projecting towards either side. The cornea has become formed, but its areolation 

 is still imperfect, and the visual elements, radiating from the ocular pigment, are 

 ■mequaUy developed, those in the middle being still quite rudimentary. The luminous 

 ascicle, distinct in the earliest stages, has now a narrow ring of red pigment coating on 

 the base. The following development of the eyes proceeds quite gradually, and as early 

 as- the Cyrtopia stages, they exhibit much the same appearance as in the adult animal, 

 though comparatively smaller and less expanded at the tip. 



