32 G- 0. Sårs. 



similar tooth is constantly found on each side of the 

 posterior part of the carapace. The free part of the body 

 immediately adjoining the metasome, and representing the 

 mesosome, has now become divided into 7 closely-set seg- 

 ments, and the ventral prominence, mentioned in the pre- 

 ceding stage, has considerably increased in size, and now 

 clearly shows itself to issue from the anterior of these 

 segments. It has, however, not yet given rise to any 

 distinctly defined limbs, these being only formed in the 1st 

 Furcilia-stage as a pair of small buds. The metasome 

 now exhibits its full number of segments, the last or sixth 

 being well defined from the telson, and at the same time 

 having given rise to the uropoda. 



The compound eyes are in process of formation, the 

 ocular pigment having assumed a darker colour, and the 

 visual elements being about to develop themselves. They 

 are, however, still wholly covered by the anterior hood-like 

 part of the carapace, and only in the succeeding stage 

 (Fur cilia) will be freely exposed and projected laterally. 



The antennulæ (fig. 5), which, as in the preceding stage, 

 are always kept extended straight in front, consist each of 

 a rather thick triarticulate peduncle, and 2 very short 

 flagella. The 1st joint of the peduncle is by far the largest, 

 equalling in length the other 2 combined, and it is produced 

 at the end outside to a strong, anteriorly-pointing spine, 

 extending beyond the middle of the last joint, and minutely 

 spinulous on the edges. The outer flagellum is uniarticulate 

 and of conical form, carrying at the tip 4 unequal setæ, one 

 of which is distinctly ciliated. The inner flagellam is some- 

 what smaller than the outer, but distinctly Particulate, and 

 is tipped with 2 small bristles. 



The antennæ (fig. 6) are still the chief locomotory 

 organs of the larva, and are accordingly very movable, being, 



