206 I. IJIMA : HEXACTINELLIDA. I. 



have here evidently a feature much subject to iudividual varia- 

 tion. Perhaps, as a general occurrence, the compression becomes 

 gradually more and more marked as the sponge grows in size. 

 Sometimes specimens of considerable dimensions may be approx- 

 imately circular in circumference for nearly the entire length ; 

 such a case is found in Spec. L (of the above list), which, being 

 preserved in alcohol and in good condition, has undoubtedly 

 retained the natural form. 



As a rule, the upper terminal region of the body may be 

 said to have a roundish form in cross-section. Spec. J (PI. VI, 

 fig. 4) is exceptional iu so far as the greater part of the body is 

 nearly cylindrical, being almost circular in cross-seclion, while 

 the upper end is perceptibly flattened, here the breadth measur- 

 ing 30 mm. in one direction and 25 mm. in the other. 



Constant seems to be the pronounced compression of the 

 body-wall at the contracted inferior extremity, where the basal 

 fibers are given off. To give the cases in which I have measured 

 the diameters at this position : 



Spec. A 8x 5 mm. 



B lOx 7 „ 



I) 12x 6 „ 



I 17x11 „ 



/. 18x10 „ 



Q 26x12 „ 



The compression at this end seems to be independent of 

 that in the upper main portion of the body, for I have found 

 the i^lanes of the two not always exactly coinciding. They may 

 be disposed even nearly vertically to each other ; so, e. g., in 

 Spec. /. 



