DEVELOPMENT AND GROWTH 33: 



lateral spines, the presence of which distinguishes this furcilia from the immediately post-larval forms, 

 to break off in those furcilias which are shortly due to moult, and this results in their inclusion with 

 the post-larvae. Although there is general agreement with John's results, the mean lengths of the 

 fifth and sixth furcilias suggest that the latter stage may frequently be omitted. In the last four 

 furcilia stages there is a gradual reduction in the number of terminal spines on the telson, from seven 

 in the fourth furcilia to five in the fifth, three in the sixth and one in the seventh and all subsequent 



Table 7. Mean lengths and ranges of length of the larval stages from first calyptopis to seventh furcilia 



E N, Nj Mn C, C2 C3 F, Fj F3 F4 Fs F f, F7 

 LARVAL STAGE 

 Fig. 13. The mean lengths (circles) and total range of length (vertical lines) of the larval stages 

 from first calyptopis to seventh furcilia. 



Stages. In furcilias which are about to moult it is sometimes possible to see through the exoskeleton 

 and to determine the number of terminal spines that will be present in the next stage (Lebour, 1926; 

 Eraser, 1936; John, 1936). It has been possible to do this for a total of 141 fourth furcilias and 

 99 fifth furcilias. Table 8 shows the number and percentage of these fourth furcilias that were going 

 to moult to fifth furcilias and the number and percentage that were going to moult directly to sixth 

 furcilias omitting the five-spined stage. Similarly, the 99 fifth furcilias have been divided according 

 to whether they were going to moult into sixth or directly into seventh furcilias. The percentages in 

 Table 8 have been used in Fig. 14 to trace the developmental paths taken by one hundred fourth 

 furcilias. Of the original hundred, nine moult to sixth furcilias and ninety-one to fifth furcilias by 



