ECHINOCYAMUS PUSILLUS. 31 



vegetative pole increase in number in such a degree that they often 

 give the impression of being arranged in several layers. Those in the 

 inner layers, which either have lost their connection so as to be free 

 or still remain attached to the wall of the Blastula by plasmatic fila- 

 ments, enter the blastocœl irregularly and accumulate at first close to 

 the vegetative pole. As may be understood from my figures, some of 

 these cells have evidently obtained a club-shaped appearance by having 

 been pushed into the blastocœl without losing their connection with the 

 point of attachment. These cells are in process of separation as future 

 wandering cells. As a rule, several such cells enter the blastocœl simul- 

 taneously. Thus I never succeeded in finding any arche-mesenchyme 

 cells in the Blastula of Echinocyamus. 



In spite of repeated immersions of the objects in different colou- 

 ring fluids, I very rarely found the cells at the vegetative pole in a 

 state of division. Only a few times did I succeed in observing cells 

 there in different stages of karyokinesis after having stained the objects 

 with Grubler's acetic acid carmine, while it is easy to get splendid 

 views of cells in division in other places of the blastoderm. If it is 

 true that cells in a state of division are rarely met with at the vege- 

 tative pole, the cells which are detached ought to be subsequently re- 

 placed by others in some way, and we may well suppose that the wan- 

 dering cells have been pushed into the blastocœl by the pressure effected 

 by the remaining blastomeres being in a lively state of division and 

 multiplication. 



In connection herewith it ought to be mentioned that I have only 

 in very few cases seen the free mesenchyme cells in the Blastula in a 

 state of division, and therefore suppose that they increase in number 

 during the blastula stage mainly by means of immigration and that it is 

 only in subsequent developmental stages of the larva that a multipli- 

 cation by division takes place. 



I never found that the wandering cells issue from any other 

 place in the blastoderm than the vegetative pole. 



Thus from what I have said above the mesenchyme cells do not 

 enter the blastocœl in any definite order in Echinocyamus, but soon after, 

 at 15 to 20 hours after the fecundation, they arrange themselves in two 

 bilaterally symmetrical heaps or bands, one along each side of the Bla- 

 stula, Fl. II, fig. 33 — 35. It seems to be a rule that most of the cells 

 which have first become free, take this symmetrical position and, besides, 

 that they differ from the cells entering later in having a more rounded 



