316 



HYALONEMA (OONEMA) BIANCHORATUM PINULINA. 



The relative thickness (thickness X 10000 : length) of the superficial 

 (dermal and gasti'al) amphioxes of different lengths of both specimens together 

 is shown in the following table : — 



This correlation between length and relative thickness comes out very clearly 



in the curve in the graph., Fig. 17. 



To ascertain whether the superficial amphioxes of varying relative thickness 

 form a continuous series I arranged the 94 measured according to this relation 

 a,nd the result is represented in Figure 18. 



The frequency-curve of the different relative thicknesses in this figure 

 clearly shows that, biometrically, two kinds of superficial amphioxes must be 

 ■distinguished: — more slender ones, in which the proportion of length to thick- 

 ness is 10000 : 74-210, most frequently about 10000 : 112, and stouter ones 

 in which this proportion is 10000 : 210-447, most frequently about 10000 : 

 312. Among the superficial amphioxes 



0.41-0.8 mm. long 82 % belong to the stout and 18% to the slender kind. 

 0.81-1.2 " " 49% " " " " " 51%" " 

 1.21-1.6 " " 27 % " " " " " 73% " " 

 1.6 -2 " " % " " " " " 100% " " 

 It is to be noted that the shortest superficial amphioxes observed, that is 

 those 0.41-0.6 nun. long, are on the whole relatively not quite so stout as those 

 0.61-0.8 mm. long, which are on the whole the stoutest. These smallest am- 

 phioxes are probably young forms. Also among the spicules 0.61-1.6 mm. 

 long there are, no doubt, some young forms of larger ones. And since the 

 larger ones are all the slender kind these young forms will probably for the most 

 part be young forms of the slender ones. 



The distal ends of the spicules of the free part of the stalk are all broken off. 

 The parts present have a maximum thickness in specimen a of 0.8 mm., in b 

 of 1.3 mm. The spiral twist, which all the long fragments exhibit, is such that 

 there is one whole turn in about 23 cm. of length. The spicules forming the 



