92 DISCOVERY REPORTS 



7th thoracic appendage. Occasionally larvae belonging to this stage are found in which 

 the process has a little spine at its tip. Th. IV is drawn in lateral aspect to showthe typical 

 flexion in the thoracic limbs. 



One large larva included in this stage had traces of the eighth limb just dis- 

 tinguishable. 



Gills (Fig. 22 d). The gill on Th. I is single lobed and small, although more notice- 

 able than in the preceding stage. Gills II-V are trilobed as in the preceding stage, but 

 with two of the three lobes in each gill more or less equal to each other and the third 

 rather short. The formation of a fourth lobe can be seen at the base of the innermost 

 lobe, and in gill II still another incipient lobe at the base of the existing middle lobe. 

 Gill VI is still bilobed but much larger than previously and has two small rounded 

 processes basally. Gill VII is bilobed. 



Pleopods. The pleopods (Fig. 22 e) are unaltered in general structure but have in- 

 creased the number of marginal setae, there being now ten to twelve instead of eight to 

 ten on the exopods. 



Luminous organs. All the luminous organs are present. 



Table XXXIV shows the incidence of larvae with four terminal spines on the telson. 

 The infrequency of occurrence of this form is comparable to that already noted (p. 88) 

 in larvae having six terminal spines, and the remarks made concerning the latter form of 

 larva are equally applicable to that having four terminal spines. 



Table XXXIV. Occurrence of Furcilia larvae with four terminal spines on the telson 



FIFTH FURCILIA 



The frequency of occurrence of larvae of this form and their average lengths are stated 

 in Table XXXV. The average length of all the larvae is 9-52 mm., and the range is 

 between 8-25 and 11-50 mm. 



The carapace (Fig. 23 a) has the rostrum less rounded and more angular in outline, 

 and there is generally a distinct short broad spine at the apex. The lateral denticle on 

 the carapace is more pronounced than in the previous stage. 



The telson length is more than five times the breadth at the insertion of the smallest 

 postero-lateral spine (Fig. 23 c). The posterior margin of the telson carries three spines 

 on a border which is much narrower and more rounded than in the previous stage. In 



