314 



HYALONEMA (OONEMA) BIANCHORATUM PINULINA. 



bent amphioxes usually enclose an angle of 130°-140°. Their bend is generally 

 situated so much nearer one end than the other that one limb is six to eight 

 times as long as the other, the spicule consequently having the appearance of a 

 promonaen. Rarely the bend lies in the middle. The tyle is, as stated above, 

 generally only 1-6 m thicker than the adjacent parts of the spicule, and in that 

 case simply oval. Occasionally, however, much stouter tyles are observed, 

 and in these cases it is clearly to be seen that the tyle is composed of from 

 one to four rounded knobs representing rudimentary rays. A few spicules 

 of this kind were triactine, a perfectly developed ray occupying the place of one 

 of the knobs. Such triactines were observed both among the superficial and the 

 choanosomal amphioxes. 



The proportion of length to thickness is in the choanosomal amphioxes 

 of both specimens together 10000 to 58-173, on an average 10000 : 109.3. 

 As the curve (Fig- 17), in which the reciprocal proportions (thick- 

 ness X 10000 : length) are represented, shows, there is no great difference 

 in the average relative thickness of the smaller and the larger choanosomal 

 amphioxes. 



In the superficial (dermal and gastral) amphioxes (Plate 82, figs. 13-19) the 

 proportion of length to thickness is 10000 to 74-447, on an average 10000 : 

 241.3. Among these the shorter are, on the whole, as the following table shows, 

 relativeh' much thicker than the longer. 



