52 



MR. L. A. BORRADAILE ON THE 



are instructive in regard to the segmentation of the phyllopod 

 limb. Here the number of the segments which are formed in the 

 endopodite varies with the limb and with the age and sex of the 

 individual. Nearly always the four distal segments can be made 

 out, and often a fifth is to be found proximal to them, leaving a 

 long basipodite, which is always clearly marked off from the coxo- 

 podite. Across the basipodite, distal to the exopodite, there 



Text-figure 24. 



ap 



5 



ex—Yy 





bas—\ 



fy 



(3+4) \ 





COX-fcf^ 





pr.cx- 



Text-figure 25. 



Text-fig. 24. Mandible of Calanus sp. 

 „ 25. Mandible of Cypris sp. 



For lettering see p. 71. 



occasionally appears an additional joint, the faintest of the series, 

 indicating the double nature of the segment*. 



* It is perfectly true that most of these segments are without muscles, but from 

 that it does not follow that their evidence may be disregarded. Probably they are 

 vestigial, having lost their endites, and not, as where the limb becomes subcylmdrical, 

 acquired a value of their own. The division of the basipodite probably occurs also 

 in Anaspides (text-fig. 12), where, in the anterior thoracic limbs, the endopodite 

 appears to contain six joints, but is flexed between the third and fourth of these, 

 not between the second and third as in the Eucarida. It seems likely that the first 



