234 "TERRA NOVA" EXPEDITIOK. 



20 mm. to 59 mm., I find that tlie length varies from 2" 2 times the breadth in the 

 smallest specimens to 1 ' 9 times the breadth in adult specimens, and that, allowing for 

 individual variation, there is a progressive change between these proportions as the 

 animal grows to the adult condition. In the same way, the length of the metasome in 

 these specimens varies between 1 • 5 times the breadth in the smaller specimens to 1 • 2 

 in the largest. 



Similarly in G. acutus, the length of the body varies between 2 ■ 45 times the 

 breadth in young specimens measuring about 20 mm. to 2 • 2 times the breadth in fully 

 grown specimens of 99 mm. In the same specimens the metasome is twice as long as 

 broad in small specimens, and only 1 • 5 5 times as long as broad in the largest specimens. 



It will be seen from these measurements that the proportions of the body and of 

 the metasome in young G. antarcticus are almost exactly the same as those of old 

 G. acutus, and the degree of " pointedness " of the metasome is very nearly the same. 

 So that if we only had young of G. antarcticus and fully grown specimens of G. acutus 

 before us, it would be almost natural to assume that the one would grow into the other. 

 On the other hand, young G. acutus and fully grown G. antarcticus are very easily 

 distinguishable. In the one, the prolongation of the point of the metasome is at its 

 maximum, and in the other it is almost obsolete. 



Size for size, therefore, the two forms are distinct, and may be identified from the 

 measurements I have given. G. acutus is a stretched or drawn-out form of G. antarcticus. 



A more constant distinction is to be found in the proportions of the joints of the 

 posterior thoracic legs. Hodgson gives as one of the specific characters of G. acutus, 

 " legs very long and slender," and a study of the figures given by him and Eichardson 

 for G. acutus and the comparison of those figures with the ones given by Pfeff'er and 

 CoUinge to illustrate G. antarcticus will bring out the differences in the proportions of 

 the joints of both forms. The diff"erence is even more obvious in the actual specimens. 

 The legs in G. antarcticus are certainly shorter and stouter than in G. acutus. But, 

 again, the differences are those of degree and not of structure. I give the actual 

 measurements of the last three joints of the last thoracic limbs of G. antarcticus and 

 G. acutus, taken from specimens of comparable size, 58 mm. and 55 mm. respectively. 

 I had no specimens of G. antarcticus larger than 5 9 mm. in the collections I examined. 



G. antarcticus. — Carpus, 9 mm. long, 4 mm. broad at its widest point ; propodus, 



9 mm. long ; dactylus, 4 ' 5 mm. long. 



G. acutus. — Carpus, 10 "5 mm. long, 2 mm. broad at its widest point; propodus, 



1 • 5 mm. long ; dactylus, 6 mm. long. 



These measurements give, in effect, the chief difference between the two forms. 

 In G. acutus, while the joints are actually longer than in G. antarcticus, their very 

 much narrower width emphasises the difference in length and makes the joints appear 

 much longer and more slender in comparison than they actually are. 



Other differences between the two forms have been pointed out by CoUinge, in the 

 degree of insertion of the cephalon into the first segment of the mesosome and in the 



