GEODIA ATAXASTRA. 



83 



AMPHIOXES 



of 



Var. angustana 



Thickness 



100 /( 



200 11 



in the 

 middle 



200 /( 



100 /( 



below one end 



below the other end 



17 /< 



20 /< 



30 IX 



20 /< 



17 /. 



Var. latana 



12 /, 



16 /( 



27 !x 



16 /( 



12 /, 



Var. lataiia 



12 /< 



17 A< 



32 /, 



25 /< 



17 !x 



In var. angustana the large choanosomal amphioxes are 1.2-2.8, mostly 

 1.6-1.8 mm. long, and 17-43, mostly 22-38 p. thick. In var. latana they are 

 considerably smaller, measuring only 0.6-1.9 mm., mostly 1.2-1.6 mm., by 12- 

 37, mostly 20-34 /<. 



I have subjected the length of the large amphioxes (and also the length 

 of the rhabdomcs of the orthoplagiotriaenes) of this species to a biometric in- 

 vestigation for the purpose of attaining an insight into the relative frequency 

 of the different lengths of these spicules. In all, the length of about a hundred 

 and fifty amphioxes of the two varieties, taken at random, were measured. 

 The amphiox-lengths within ranges of 0.1 mm. (from 0.45-0.55 mm., from 0.55 

 to 0.65 mm., and so on) were counted, these numbers reduced to percentage, 

 and the percentage frequency-numbers thus obtained plotted on the ordinates 

 erected at the points of the horizontal axis indicating the amphiox-lengths (of 

 0.5 for 0.45-0.55 mm., 0.6 for 0.55-0.65 mm., and so on). By connecting the 

 points thus plotted the two curves for the two varieties (Fig. A) were obtained. 



Per cents of all the 

 large rhabds measured. 



oo 



IS 



4S- 



10 



















































/ 





















r 



/ 



\ 



\ 

 \ 













/ 



✓ 



/ 



A 



\ 



/ 

 1 

 1 

 1 







\ 



\ 



\ 









1 



1 



1 



1 



1 



/ 





V 

 \ 



/— 



/ 



.-J / 







— V- 

 \ 



V 



\ 



\ 



p. « 







,^ 



Fig. A. 



' mm. in length 



Percentage frequency of lengths of the large choanosomal rhabds (chiefly amphioxes) measured 

 Geodia ataxastra var. angustana, Geodia ataxastra var. latana. 



