88 DISCOVERY REPORTS 



with the beginnings of a third at the base of the inner lobe, and that on Th. VII is a 

 single lobed process bearing the luminous organ on the peduncle (Fig. 20 k). 



Pleopods. All the pleopods are setose, proportionately longer than in the preceding 

 stage and have the endopod longer in relation to the exopod (Fig. 20 /). The pleopods are 

 more setose, with eight to ten setae on the exopod instead of six to eight as in the largest 

 larvae of the preceding stage. Pleopod V is more nearly similar to the remainder, but the 

 inner ramus is still less developed than the others. The appendix interna is a digitiform 

 process furnished with hooks. 



Luminous organs. In addition to the light organs present on the largest larva 

 belonging to the previous stage, the organ of Th. VII can now be distinguished (Fig. 

 20 k vii). 



Table XXXII records the occurrence of larvae having six terminal spines on the 

 telson. As stated on p. 51 above, larvae with an even number of terminal spines are 

 in their general structure intermediate between those having respectively one more and 

 one fewer telson spines. The infrequency of occurrence of the six spined form compared 

 with those having seven and five shows that the former number must be regarded as a 

 rare abnormality. 



Table XXXII. Occurrence of Fiircilia larvae with six terminal spines on the telson 



FOURTH FURCILIA 



The frequency of occurrence and average lengths of larvae belonging to this stage are 

 stated in Table XXXIII. The average length of all the larvae is 8-oi mm., and the range 

 between 6-67 and 9-92 mm. 



The rostrum (Fig. zi a,h) is more elongate and narrower than in the previous stage 

 and may have a small denticle at its apex. The lateral denticle is present. 



The telson (Fig. 21 d)is about four times as long as broad, bearing five terminal spines 

 and three postero-lateral spines. The innermost postero-lateral is more modified than in 

 the previous stage (Fig. 21 c)\ the broadened portion extends much nearer to the tip and 

 the setae are missing from the inner margin proximally. The uropods extend beyond 

 the lateral spines on the telson and may have one or two more setae than in the 

 previous stage. 



