210 ME. STAKLET W. KEMP — BISCATAN PLANKTON : 



from three to five teeth, the posterior of which, although in some cases small and sharp, 

 appears to represent the hlunt spine present in the two preceding stages ; ventrally the 

 rostrum is unarmed. The median spine at the posterior edge of the carapace persists, 

 although of comparatively small size, in the larger examples ; the minute spinules on the 

 inferior hinder margin of the carapace are present in the smaller specimens only. The 

 elhow on the 3rd abdominal somite is as prominent as in the preceding stage, and the 

 6th somite is two and a half times the length of the 5th or slightly more. The telson 

 (figs. 22 & 23) is at least three and a half times as long as wide; in younger specimens it 

 is apically emarginate, in older forms more or less truncate. Of the eight original pairs 

 of seta?, two have been carried up the sides of the telson and have become dorso-lateral 

 spinules, others being added during succeeding moults. The apex is thus left provided 

 with six pairs, two of which, the second and fourth counting from the outer angle, are 

 now much stouter and longer than the rest. 



The eyes (fig. 16) are still relatively large, one-half the length of the carapace or rather 

 less ; as in both the previous stages, the cornea is by far the widest part. The basal joint 

 of the antennular peduncle is proximally much widened on its outer edge, this widened 

 part being produced forwards to an acute point representing the lateral process ; this point 

 does not reach forward more than one-third the length of tlie basal joint. The two 

 flagella in large specimens are about equal and almost as long as the peduncle. The 

 antennal scale (fig. 13) reaches almost to or beyond the end of the antennular peduncle : 

 the flagellum is of varying length, in large examples reaching as far forward as the 

 flagella of the inner antennse ; it possesses two well-marked basal segments. The 

 antennal peduncle is two-jointed. 



All the five pereiopods with their exopods have now appeared. Pleurobranchs are 

 present at the base of all five, the arthrobranchs being still rudimentary and represented 

 by buds. Epipods are in evidence at the base of the first three pairs. The legs are all 

 of roughly the same length and are but little longer than their exopods ; their respective 

 joints bear much the same proportion to one another as those of the adult, with the 

 exception of the dactylus of the 5th pair, which is as long as that of the 4th. The first 

 two pairs are not chelate and no traces of the spines on the inferior border of the ischium 

 and merus of the last three pairs are yet to be observed. 



The two remaining specimens in the collection, of 123 and 12-5 mm., represent the 

 post-larval stage to which Coutiere has given the name of " parva" (PI. 14. fig. 24; 

 PL 15. fig. 1). The smallest specimen of this stage that he found measured only 10*5 mm. 

 It will be seen from the table that some examples in the previous stage attain a length of 

 over 13 mm. This very considerable overlapping of the lengths of the oldest larval and 

 youngest post-larval stages is remarkable, but when the extraordinary variation of the 

 adult is considered it must be admitted that it would be even more remarkable if some 

 sort of variation did not also extend to the development. 



By far the most noteworthy feature of the change to the parva form is the great 

 reduction of the eye (fig. 17) *. It is now less than one-third the length of the carapace 

 and the cornea is not so wide as the stalk. A rather obscure convex disc situated on the 



* Figs. 14, 15, 16, and 17 are drawn to the same scale and show the growth and subsequent reduction of the eye. 



