I. '08. 62 



Development. 



Among several extremely young examples of this species, 

 caught oft* the west coast of Ireland in February, 1906, is one 

 measuring only 10 "2 mm. This specimen is of the greatest 

 interest, for although by the presence of a small number of 

 photophores in the usual positions it is at once recognised as 

 a young A. debilis, it is nevertheless a typical larva. It had 

 been previously thought (cf. Coutiere, loc. cit.) that this species 

 dift'ered in a most remarkable way from the allied form, A. 

 purpurea, in that the young left the egg in a post-larval con- 

 dition. ^ The large size of the egg when compared with that 

 of A. purpurea gave an air of probability to this view, and it 

 is doubtless true that the period of larval life is much shorter 

 in A. debilis than in the allied species. 



The larval specimen of 10'2 mm., PI. VI, fig. 5, presents 

 a very different appearance from post-larval individuals only 

 2'5 mm. longer. The rostrum is extremely short, only very 

 slightly longer than the eyes ; it is arched above and, of course, 

 shows as yet no traces of teeth. The carapace is not at all 

 laterally compressed and is about half the length of the abdo- 

 men and telson. Dorsally it is faintly carinate in its anterior 

 half ; there is a blunt prominence at the base of the orbit and 

 the antero-lateral angle is sharp and spine-like. 



The abdominal segments show no trace of carination, and 

 none of them are produced backwards in the dorsal line to 

 form spines ; the sixth somite and telson combined are almost 

 three and a half times as long as the fifth. The telson (fig. 

 7) closely resembles that found in a true zoea, it is broadly 

 lamellar, apically rounded and emarginate, and is furnished 

 with seven pairs of spines. The uropods are not free in this 

 stage. 



The eye is almost globular, about one-sixth of the length of 

 the carapace in diameter ; the cornea is rather small and faintly 

 pigmented. The antennualr peduncle is a trifle shorter than 

 the antennal scale ; the basal joint is about twice the length of 

 the two others combined and the rudimentary flagellum is 

 scarcely longer than the terminal peduncular joint. The 

 antejinal scale (fig. 8) is about two-fifths the length of the 

 carapace and slightly more than twice as long as wide ; apically 

 it is broadly lamellar and only show^s faint indications of a 

 distal spine. The antenna is only about half the length of the 

 scale ; it is swollen basally, but the proximal joint is not marked 

 off' from the flagellum. 



The mandible consists of a simple lobe, without teeth; no 

 trace of a palp was observed. The second maxilla (fig. 12) 

 consists of a basal portion which is four-lobed on its inner 

 aspect, a lamellar exopod and an unjointed endopod. These 



1 Coutiere has, indeed, figured his 30uiigest post-larval specimen 

 (11 mm.) tucked away inside the egg, in order to prove that it 

 could have been little, if at all smaller, when it was hatched. It must be 

 admitted, however, that the eggshell is an uncomfortably tight fit for 

 the specimen in question. 



