GEODIA ATAXASTRA. 



83 



AMPHIOXES 



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

 1.6-1.8 mm. long, and 17^3, mostly 22-38 /x 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 u. 



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

 of the rhabdomes 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. 



30 



~. •» »^ !> 



SoS'S^?^V?>-^>''«-^ V""'*"''^'*'' mm. In length 

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

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



