,. DISCOVERY REPORTS 



In this respect it is interesting to note that Herdman (1910, p. 21) records a specimen of the soUtary 

 form taken at 67° 5' S., 179° 30' E. which had muscle bands narrower than those of his other speci- 

 mens. Subsequent examination of the Discovery material has shown such specimens to be S. gerlachei 

 and it thus seemed worthwhile to measure the width of the muscles in S. thompsoni and S. gerlachei 

 and see whether there was any significant difference between them. For this purpose a micrometer 

 eyepiece was used and a measurement was made of body muscle IV in both the aggregate and solitary 

 form of each species. The data are shown in Text-figs. 7 and 8. It must be remembered that muscle 

 width, unlike the muscle-fibre number, which remains constant throughout the life of the animal, 



4-5 



40 



3-5. 



' JO 

 i 

 ■ 25 



u 



CO 



i20 

 1-5. 



10 

 OS. 



SOLITARY 



I S thompsoni 

 I S geriochei 



O 



O 



o o 



o' 



o 

 ,0 o, 



8 

 o o 



^ 08 



o, 



'o 



o 



o o© 



o 



On „ O O 



O OOg Oq 



o 00 

 00 00 Oo g o 



„o O O Oo , . t. 



• • • 



qOOoo^ °* • • 



oo o" oo • • 



• 



".» 



o 

 o 

 o 

 o 

 o 



t 



••I 



o 

 o 



o 

 o 

 o 

 o 



o 

 o 



o 

 o 



o o 00 °ooOo 8 



0.0 



10 



20 



25 



30 35 40 45 50 55 faO 



BODY LENGTH. Onms 



65 70 



75 



80 



65 



90 



95 100 



Text-fig. 7. Variation in the width of M. IV with body length in the soUtary forms of 5. thompsoni 



and S. gerlachei. 



40 



Q 



5 



35 

 30. 

 25 

 20 

 15 

 10 

 OS 



AGGREGATE 



O 8 



o 

 -o o 



O 0° °0 

 0^0 §0 «oo 



o 



o 



o o 



° Q ° 





|8|S 



.a^-r* 



o o 



o o 



OnO 



O S. thompsoni 

 • S geriochei 



10 15 20 25 



BODY LENGTH onms) 



30 35 40 45 50 55 60 



Text-fig. 8. Variation in the width of M. IV with body length in the aggregate forms of 5. thompsoni 



and S. gerlachei. 



