90 Charles W . Hargitt. 



of these and other phases of the problem would lead too far 

 afield, and we must satisfy ourselves for the time by the reflection 

 that while such speculations are interesting as well as ingenious 

 they are far from demonstrations. 



IV. HISTOLOGY. 



A brief study of the histology of the regenerated organs shows 

 the various stages of the process and establishes beyond doubt a 

 true histogeny, though it has not been possible to demonstrate the 

 details of mitosis in the proliferating cells. This may be due in 

 part to lack of just those refinements of technique necessary to 

 bring out these features. Some of the tissues were fixed by means 

 of Flemming's solution, some by corrosive-acetic acid, and still 

 others in lo per cent, formol in water. I have not been able 

 to distinguish that there was any appreciable advantage in the 

 one over the others, the formalin seeming to afford equally good 

 fixation and preservation. Heidenhain's iron haematoxylin and 

 an aqueous solution of haematein both afforded fairly good differ- 

 entiation, though they failed as to the nervous tissues, a result 

 which was not unexpected. 



In Figure 2 is shown a longitudinal section of a regenerated 

 rhopalium at a comparatively early stage, when first distinguish- 

 able as a minute papilla. In an earlier part of the paper I have 

 referred to its early appearance as having the character of a solid 

 bud from the upper angle of the notch made in the process of 

 excising the organ. From an examination of this figure, which 

 is among the earliest stages I have been able to satisfactorily sec- 

 tion, it would seem that in its origin it probably follows the usual 

 process of the regeneration or development of such organs in the 

 coelenterates, namely, that of budding, involving both ectoderm 

 and entoderm. As shown in the figure, there is here a typical 

 outgrowth from the distal end of the radial canal and, as also 

 mentioned in another connection, it was easy to demonstrate at 

 about this stage of development in the living medusa an active 

 circulation in the bud. The cells of the ectoderm at this stage 

 are of approximately uniform size over the entire organ, and 

 the same is also the case with the cells of the entoderm. There 



