THE Db:VELOPMENT OF LEPIDOSIREN PARADOXA. 447 



nuclei) tends to concentrate round the nerve-trunk^ so that 

 the latter now (fig. 12 c) lies embedded in a thick strand 

 of the reticulum. The protoplasm forming this contains yolk 

 granules^ and doubtless serves to supply the nerve-trunk with 

 nourishment. The nerve-trunk is in need of this, for it is 

 growing actively, both in length — as the muscle-cells are 

 pushed farther and farther away from the spinal cord — and 

 also in thickness. Whereas at Stage 24 the nerve-trunk 

 measured about 1 ^ in diameter, now it measures about 5 /i. As 

 the fibrils composing it do not appear to have undergone a 

 corresponding thickening they must have increased in 

 number. As to how this increase takes place, whether by 

 splitting of original fibres or by formation of new fibres by 

 the surrounding protoplasm, it is obviously impossible to 

 make definite assertions, based merely on observation, which 

 shall be at all reliable. Theory, of course, would favour the 

 first view. 



As regards the sensory nerves, I do not propose to say 

 anything at present, except that my evidence, so far as it 

 goes, points to exactly similar processes taking part in their 

 development as I have just outlined in regard to the motor 

 nerves. 



General Eemarks. 



Effect of Light upon the Chromatophores. 



It will be possible from the present paper to form a clearer 

 idea of the process of change in the chromatophores to which 

 I alluded in my description of the external features. I still 

 hold to the view that we have to deal with an actual 

 retraction of pseudopodia, and not a mere movement of 

 pigment granules into the body of the cell as held by 

 Ballowitz. Stray pigment granules may be observed fre- 

 quently remaining where the pseudopodia have been. I take 

 these not as indicating that the coll processes are still pro- 

 truded, but as having been left behind by the pseudopodia 



VOL. 46, PART 3. NEW SERIES. K E 



