No. I.] CONTRIBUTION TO INSECT EMBRYOLOGY. 85 



in length, while the neuroblasts remain to all appearances un- 

 altered. The increase in the number of daughter-cells is so 

 great that they are forced to arrange themselves in several 

 rows. In the figure this is best shown in the progeny of the 

 innermost neuroblasts, and the tapering columns there formed 

 may be regarded as typical. 



In my preliminary note ('9i*=) I held that the daughter-cells 

 themselves divide to form the multiple rows in each pillar. I in- 

 cline to think that I was mistaken on this point. The daughter- 

 cells probably never divide but are directly converted into 

 ganglion cells. All reproductive powers seem to be confined to 

 the neuroblasts. Some of the nuclei of the daughter-cells exhibit 

 peculiar chromatic structures which I may have mistaken for 

 caryokinetic figures ; this being an easy error to make in the 

 case of small cells killed by means of heat, since the achromatic 

 portions of the spindles are obliterated by this method. 



The last stages in the proliferation of the neuroblasts are 

 shown in Fig. 31, which is taken from an advanced embryo 

 (Stage J). The columnar arrangement is no longer visible 

 since the individual cells are now converted into the de- 

 finitive ganglionic elements. On the outer periphery of the 

 ganglia, however, neuroblasts are still to be found, and ex- 

 tending from them short series of small flattened cells {g"), 

 their latest progeny, still distinguishable from the ganglion 

 cells by their deeper stain. It will be noted that these cells, 

 which like their precursors will become ganglion cells, are no 

 longer budded off at right angles to the surface of the nerve- 

 cord but parallel to it, a condition undoubtedly due to a lack 

 of space. Finally the neuroblasts stop proliferating and shrink 

 to the size of their progeny. Their chromatin then shows 

 signs of senility. Beyond this point I have been unable to 

 trace them satisfactorily. They are probably broken down and 

 absorbed by the growing ganglion cells. Some of them may 

 persist as ganglion cells of a particular character and function, 

 though I deem this improbable. 



The dermatoblasts play an important part in the develop- 

 ment of the ventral nerve-cord, as will be seen by returning to 

 the younger stages. We left these cells as a layer covering 



