DEVELOPMENTAL PHASES 353 



Furcilia stages 



Twenty-five furcilia instars were encountered. If the same terminology is adopted for all four 

 species of Nyctiphanes as for N. simplex (Boden, 1951), the total number of furcilia types in each species 

 is as follows: N. couchii 15, N. simplex 16, N. australis 24, N. capensis 25. For N. simplex it was sus- 

 pected that three other types may occur. Frequency distributions of the N. capensis instars are given 

 in Fig. 7. 



In the case of N. simplex and N. capensis six of these types were dominant and are regarded as 

 stages or successive instars, while the remainder are considered variants. According to Gurney 

 (1942) it seems highly probable that there are six stages in N. couchii too. While Sheard recognizes 

 only three stages in N. australis, it is possible to interpret his data differently. Table 7 shows the course 

 of development of three species of Nyctiphanes and it can be seen that they are fairly similar. 



Of very great interest is the fact that two of the species do not conform to the rule first shown by 

 Fraser (1936) that the pleopods first appear as non-setose rudiments and these rudiments become 

 setose at the next moult. N. capensis and N. simplex develop setose pleopods directly in stage II on 

 somites which bore no non-setose rudiments in stage I. 



The six stages of N. capensis encountered are as follows : 



First furcilia. Pleopods non-setose. Second antennal endopod simple. 



Second furcilia. Pleopods mixed. Second antennal endopod simple. 



Third furcilia. Pleopods setose. Five terminal spines on telson. Second antennal endopod 

 simple. 



Fourth furcilia. Pleopods setose. Three terminal spines on telson. Second antennal endopod 

 simple. 



Fifth furcilia. Pleopods setose. Three terminal spines on telson. Second antennal endopod 

 segmented. 



Sixth furcilia. Pleopods setose. One terminal spine on telson. Second antennal endopod 

 segmented. 



First furcilia. Twenty-two specimens examined. Twelve measured (Fig. 8a-g). Length range 

 2-2-2-8 mm. ; average length 2-5 mm. 



The following types of furcilia are included in this stage. Those with (a) no pleopods, (b) one pair, 

 (c) two pairs, (d) three pairs, (e) four pairs of non-setose pleopods. No specimens with five pairs of 

 non-setose pleopods were encountered. The occurrence of the above types was as follows: (a) 199, 

 (b) 35, (c) 34, (d) 18, (e) 6. 



There is no rostrum. The frontal plate is broader than long with a small, distinct, emargination of 

 the anterior border. There is a small, but definite, denticle on the inferior margin of the carapace 

 toward the posterior end. The eyes are heavily pigmented and project beyond the edge of the 

 carapace. 



The first antennal peduncle has three segments and the basal segment bears a strong spine, reaching 

 just beyond the middle of the third segment, on its anterior outer margin. The rudiments of the two 

 flagella are present on the third segment. 



The second antenna is biramous, natatory, and its endopod is simple. 



The usual condition of the thoracic appendages is that the first and second maxillae are clearly 

 visible, the first cormopod is present and bifurcate, and the bud of the second cormopod is free but 

 naked. The remaining cormopods are contained in the integument and difficult to discern. Individuals 

 in which the pleopods are developed frequently have the second cormopod present, bifurcate and 

 with bilobed gill rudiments. 



