212 JOUKNAL OF ENTOMOLOGY AND ZOOLOGY 



6 the naupliar appendages are better marked and may be consid- 

 ered to be the three large paired areas below the optic lobes. In 

 Figs. 10 and 1 1, the brain region is outlined; there are also in these 

 stages indications of the various ganglia more or less opposite their 

 appendages. In Fig. 8, many appendages are evident, and there 

 are many more segments than in earlier stages. At this time the 

 segments are similar, the brain and optic lobes show and the mouth 

 area is seen. Fig. 9 shows a typical pair of body ganglia of a 

 slightly earlier stage. At such a stage the ganglia seem made of 

 two pairs. In Fig. 10, the naupliar appenciages have changed posi- 

 tions and there is a long series of closely applied appendages similar 

 to those in Fig. 8. Figs. 12 and 13 show considerable shifts in the 

 upper appendages. The lack of harmony between the results of 

 McMurrich and these may be easily explained. The adult isopod 

 has the following appendages: (1) Antennules, (2) antennae, 

 (3) mandibles, (4) first and second pairs of maxillae, (5) one pair 

 of maxillipeds, (6) seven thoracic legs, (7) six abdominal append- 

 ages. The appendages, as alreadv shown, are first developed in 

 the head region and then added to from the caudal end. At a time 

 of a maximum number of appendages and segments the appendages 

 are much alike, but there are differences in size, and at a later time 

 there are changes in position. In the region of the third and 

 fourth appendages there is a great crowding, so that segments may 

 be fused and appendages covered. This is shown to some degree 

 in Figs. 12, 13, 14, and 15. McMurrich failed to recognize this, 

 and he apparently counted in the first thoracic leg as a maxilliped. 

 The biramous structure of Figs. 12 to 15 is really the first thoracic 

 leg, as is clearly shown in Fig. 13. Other legs of these stages may 

 be seen to be biramous when separated from each other, but this 

 first thoracic leg seems to retain this condition longest and remains 

 small for a long period. 



McMurrich failed to call this a leg, and yet had the right number 

 of legs ! This probably came about through another slight over- 

 sight. At one period preceding Fig. 13 each segment has an 

 appendage, but after a time the last thoracic or first abdominal 

 segment, whichever it is, loses its appendage. This is the seg- 

 ment which seems to have been counted in by McMurrich to bring 

 up the right number of legs. 



