DEVELOPMENT OF E. TRIACANTHA 283 



There is a strong posterior dorsal spine on each of the third to fifth abdominal so- 

 mites as in the succeeding stages and the adult (Fig. 38 f). 



The telson is narrower distally than in the previous stage and the innermost pair of 

 postero-lateral spines, still the longest, are beginning to thicken at the base (Fig. 38 d). 



Fiircilia, stage IV (Fig. 38_§') 



Description based on the examination of ten specimens. Eighty were measured and were 

 6-5-9-2 mm. long. 



In this stage the antennal endopod is segmented and there are seven terminal spines 

 on the telson. 



The frontal plate is a little more reduced, the rostral spine a little stronger, than in the 

 previous stage. The spine reaches as far forward as the end of the basal segment of the 

 antennular peduncle. The carapace has a conspicuous dorsal organ. 



The antennular spine is as long as the sum of the second and third peduncular 

 segments. 



The mandibular palp is elongated ; it may be non-setose and not segmented or be- 

 ginning to segment, but it is more often segmented and setose. 



The degree of development of the thoracic limbs is as follows : 



First limb. Endopod of five segments and long, reaching beyond knee of second, not 

 kneed or feebly kneed. No gill bud. 



Second to fourth limbs. Endopods long and kneed. 



Fifth limb. Endopod considerably shorter than fourth, of five segments, not kneed 

 or feebly kneed. 



Sixth limb. Short. Endopod usually of three, sometimes of more segments, setose. 



The first limb has no gill bud. Those of the second to fifth are of two nearly equal 

 branches and a third smaller or much smaller branch. The sixth gill bud is of three 

 nearly equal branches with or without a fourth and smaller branch. The seventh is of 

 three larger and one or two smaller branches, or of four larger branches with or without 

 the buds of other branches ; the eighth of two nearly equal branches with or without buds 

 of others. 



The end of the telson is narrower than in the previous stage and the innermost of the 

 three pairs of postero-lateral spines are still wider and stronger (Fig. 38^). 



Furcilia, stage V (Fig. 38 h, i) 



Description based on the examination of ten specimens. Thirty-nine were measured and were 

 7-5-IO-2 mm. long. 



In this stage there are five terminal spines on the telson. 



The frontal plate is further reduced, the rostral spine so strong that it is more 

 appropriately called a rostrum. It reaches nearly to or to beyond the end of the first 

 segment of the antennular peduncle; a strong crest runs centrally down it from the 

 dorsal organ (Fig. 38 h, i). 



