DEVELOPMENT OF E. TRIACANTHA 279 



level of the eyes to form strong postero-lateral wings. There is a short but stout posterior 

 projection from the middle of the hinder edge of the carapace. 



The antennular peduncles are sometimes unsegmented, but are most often of two, 

 sometimes of three, segments. The flagella are represented by small single segments. 



The antennae, mandibles, first and second maxillae and first thoracic limbs are 

 present as in other species of Euphausia for which this stage is known and are of similar 

 structure. The thoracic segments without limbs are clearly visible as encircling folds of 

 the integument. 



The abdomen is of six segments. The telson has seven terminal spines decreasing in 

 size from the outer to the inner, each having a row of spinules along each lateral margin. 

 The three postero-lateral spines increase in size from the outer to the inner and each has 

 a secondary spine, apart from spinules, arising from it. 



Third Calyptopis (Fig. 38 b) 



Description based on the examination of fifteen specimens. Thirty-three were measured and 

 were 3 -0-3 -6 mm. long. 



The carapace rises dome-like mid-dorsally to a point surmounted by a large and con- 

 spicuous dorsal organ. It is very broad anteriorly, with the margin gently rounded, 

 usually with a tiny spine in the centre ; it is arched over each eye, constricted behind the 

 eyes and then widened out into the postero-lateral wings. There is a strong median 

 projection from the posterior margin which rises dorsally. A pair of lateral denticles is 

 present. 



The antennular peduncle is of three segments ; the spine arising from the outer distal 

 corner of the basal segment is considerably longer than the sum of the second and third 

 segments. 



Buds of the second thoracic limbs are usually, though not invariably, present as large 

 conical protuberances. 



The abdomen is of seven segments. The posterior lateral margins of the sixth seg- 

 ment are produced backwards to form a pair of short spines, one running down either 

 side of the telson ; they become longer in the Furcilia and are present in post-larval 

 stages but not in adults. The telson is broader than in the second Calyptopis ; the ter- 

 minal spines remain unchanged. The innermost of the postero-lateral spines is the 

 longest, the outer the shortest; each of the three has a secondary spine arising from it; 

 the inner two, but not the outer, have a row of spinules along the inner margin. 



Furcilia, stage I (Fig. 38 c) 



Description based on the examination of twenty specimens. One hundred and forty-six were 

 measured and were 4-0-5-3 mm. long. 



In this stage there are four pairs of non-setose pleopods. 



The frontal plate is shield-like with the centre of its rounded anterior margin pro- 

 duced into a short but strong spine, the rostral spine. The carapace has a very con- 



