ON THE ANATOMY OF HISTKIOBDELLA HOMARI. 339 



fibrillge, that thread their way aniOHg the crowded alveolar 

 spheres. In my best preparations the astral rays appear like 

 wires bending to and fro among the alveoli" (p. 13). "From 

 a study of Toxopneustes one would be led to the conclusion 

 that they ^arise in rows of granules or microsomes, held 

 together by the continuous substance" (p. 15). These words 

 exactly describe the appearance of the astral rays in the 

 living egg of Histriobdel la. 



Towards the centre of the astral figures the rays appear as 

 continuous fibres, while peripherally they break up into rows 

 of granules. I believe in both the asters and the central 

 spindle the granules do not build up the achromatic figure, 

 but are merely incidental to it. This is borne out by the fact 

 that they are less numerous within it than in the surrounding 

 cytoplasm. For this reason the area of the amphiaster in the 

 living egg is always the most ti-ansparent. The archoj^lasra 

 can be distinctly seen as a clear substance running between 

 the microsomes. 



The less dense nature of the astral rays, as compared with the 

 Hbi'es of the spindle, has been clearly demonstrated recently by 

 Lillie (18) on centrifugalised eggs, where the egg-granules are 

 readily driven through the substance of the astral rays, while 

 they are stopped and forced to go round that of the spindle. 



The chi'omosomes in Histriobdella are arrano-ed round 

 the periphery of the equatorial plate. Each chromosome lies 

 directly against one of the spindle-fibres. These run from 

 one centrosome to the other without any break in their con- 

 tinuity. It is obvious that the chromosomes have no proper 

 mantle-fibres, and that the number of fibres composing the 

 spindle is in excess of that of the chromosomes. In sections 

 the number of fibres can be counted. There are twenty, 

 while there are only eight chromosomes. 



The centrosome itself is not distinguishable »s a distinct 

 point or granule iu the living egg, but its position is indicated 

 by a small area where the fibres of the astral rays and those 

 of the spindle all converge on one another. No sphere can 

 be distinguished. 



