470 ROBERT GURNET. 



gillsj which perhaps become functional at this stage. The 

 first and second maxillipedes retain their original form, but 

 the exopodite bears now twelve seta) instead of six at its 

 distal extremity. Each bears also at its base a small 

 epipodite, but there is as yet no trace of gills. The succeed- 

 ing six pairs of thoracic limbs are all well developed, and 

 show distinct joints beneath the cuticle. The third maxilli- 

 pede is the only one that bears an exopodite — a simple 

 unjointed process, — the others developing directly to the 

 adult form. 



The gills of the posterior thoracic region (fig. 8) are all 

 distinctly formed except that the podobranch of the third 

 maxillipede is not yet separated from the epipodite. As yet 

 also they have not acquired the lamellate form of the adult 

 gill. In the abdomen the pleopods are further developed on 

 the last five segments, each being about half the length of 

 the segment succeeding it. The lateral spines of the seg- 

 ments are now more conspicuous than before. 



The telson at this stage (fig. 5) has generally developed a 

 new pair of setae on its internal edge in front of the others, 

 but in some specimens the number was found unequal on the 

 two sides, the formula being normally 8 + 8, but occasionally 

 8 + 7. 



Fourth Stage (fig. 7). — Measurements (average and 

 variation in fourteen specimens) : 



