DEVELOPMENT, GELASIMUS AFTER HATCHING 495 



have become more prominent. The border of the carapace bears 

 a series of straining hairs which serve to keep foreign particles from 

 getting under it. 



The fifth zoea (figs. 12 and 13) has increased in size to a length 

 of 2.25 mm. The antennule (fig. 25) shows the following changes : 

 a rather deep constriction divides the distal portion from the 

 slightly enlarged basal portion; on the distal portion the number 

 of hairs of the second series is increased from the single one to 

 three. When this stage is nearing its molting time, the distal 

 portion shows indistinctly tw^o or three constrictions where the 

 joints of the next stage will appear. In the antenna (fig. 33) 

 the flagellum is bisegmented and is marked off by a joint. As the 

 time for the next molt approaches, the flagellum shows indica- 

 tions of about twelve constrictions which mark out the joints of 

 the next stage. The first maxilla shows a few minor, but inter- 

 esting changes (fig. 50). There is developed on its lateral border 

 a rounded low prominence which bears a single sparsely plumose 

 stout hair similar to those found on the coxopodites of the maxil- 

 lipeds at the base of the epipodite. Between the palp and the 

 epipodital prominence is a peculiar, densely plumose hair similar 

 in structure to the hair on the distal segments of the endopodites 

 of the first and second zoeal maxillipeds and to the so-called 'audi- 

 tory hair' of Mysis. The exopodites of the first and second maxil- 

 lipeds bear ten hairs (figs. 66 and 67). The endopodite of the 

 second maxilhped has grown considerably larger. The third 

 maxillipeds and the periopods are finger-shaped appendages, and 

 two or three small buds dorsal to their bases are the early gills. 

 The pleopods are also finger-shaped and show indications of divi- 

 sion into protopodite, exopodite, and endopodite, although the 

 endopodite is exceedingly minute. The telson bears four pairs of 

 plumose spines. During the last day or two of this stage a 

 number of changes are noticeable in preparation for the next 

 molt. The soft part is withdrawn from the dorsal spine, until it 

 is entirely empty, and from the anterior spine until it fills the 

 basal fourth only. The exopodites of the maxillipeds are 

 shrunken away from their coverings, thus accounting for the 

 sluggishness of the larva at this time. All the joints of the perio- 

 pods are differentiated. 



