140 I. IJIMA : HEXACTINELLIDA. I. 



owing to shrinkage caused by the action of the reagents. I think 

 it is approximately cylindrical in the natural state. In the 

 preparations that shape is sometimes retained ; but more frequently 

 the collar either gradually narrows toward the distal end or is 

 somewhat narrowed in the middle section, in which latter case 

 the distal end is often expanded in a funnel-like manner. The 

 flagellum traverses the collar either at its middle throughout or 

 along one of its lateral edges after having inclined to that side 

 at a certain distance away from the origin of the flagellum in 

 the center of the distal nuclear surface. In height the collar 

 measures 0-6/7. (5.6 // on an average). The breadth usually 

 measures only IY2-2 // (1-7 /^ on an average), i.e., about as much 

 as the diameter of the nucleus. It may however occasionally 

 reach 3 /^ at the base or at the expanded distal end of the collar. 

 In one or two instances I have seen a line apparently 

 stretching itself between and connecting the flaring rims of a 

 few consecutive collars, which line reminded me at once of Sollas' 

 membrane. But I have satisfied myself that it is to be regarded 

 as something accidentally produced, — possibly a flagellum or 

 portions of flagella laid down upon the free ends of the collars. 

 The collars stand out freely and solitarily, being separated from 

 one another by a comparatively wide space whose width may be 

 said to be on the whole about equal to the distance between the 

 nuclei of the respective choauocytes. 



Observations of the chamber-wall in the fresh state, 2-5 hours 

 after the capture of the specimens, did not reveal anything of 

 much importance. The preparation of a piece of the fresh 

 choanosome for examination under the microscope necessarily 

 involves more or less dislocation of spicules from their proper 



