1906.] 



Cell Communications between Blastomeres. 



501 



activities of the parts of the embryo," they form as thread-like pseudopodia 

 of the hyaloplasm similar to the way Kadiolaria and Foraminifera throw out 

 this layer in the formation of their long and delicate processes. In some 

 cases and possibly in all cases except where they form as already mentioned 

 as the drawing out of established connections, my own observations also lead 

 me to believe they are essentially of the nature of pseudopodia. 



In the living egg they are plainly seen to possess pseudopodium-like move- 

 ments, varying in shape and size from time to time. As in the pseudopodia 

 of Gfromia oviformis, the classical object of study, the granules of one thread 

 are plainly seen to pass into another where they touch or overlap, so the 

 granules in the protoplasm of the blastomeres can be traced along these 

 strands from one cell to the other. Frequently the strands have a beaded 

 appearance not unlike the appearance of the pseudopodia in Orbitolitcs after 

 stimulation. 



In the Annelid Podarke, the egg of which is about the same size as that of 

 Hwpomatus, and has a form of cleavage as far as I can determine very 

 similar step for step, it is interesting to note that Treadwell (13), in speaking 

 of the 40-cell stage, says " strands of protoplasm can be plainly seen 

 reaching across the cleavage cavity " and " protoplasmic connections do exist 

 between blastomeres of relatively late cleavage stages " (p. 410). His text- 

 figures 3 and 4, show two strands crossing the segmentation cavity from the 

 apical rosette cells and joining two of the entomeres, here, as Treadwell 

 suggests, possibly the contact between them from an early stage has never 

 been broken. 



During segmentation, the egg of Eupomatus seems to have alternate 

 periods of rest and rapid division. During the periods of rest the cell 

 boundaries seem to fade out, and the nuclei become large and peculiarly 

 opaque. Cutting sections of eggs in one of these resting periods, no 

 matter how well fixed, it is next to impossible to distinguish cell outlines, 

 and in the early stages the egg looks not unlike a multinucleated mass of 

 protoplasm. I have noticed that the first signs of the assumption of the 

 period of division are shown, by the reappearance of the cell outlines, when 

 the cells seem drawn apart from one another to some extent. It is at this 

 time that the filaments are most obvious and numerous. When the period of 

 active division has fully set in they are seldom seen.* 



Frommann (2) years ago drew attention to fine lines running between the 



* These periods of rest and active division are used as applying to the appearance 

 presented in preserved material. I am not certaiD that they are to be distinguished 

 during life. As far as I have observed, growth is steady, although material preserved at 

 intervals shows these alternating periods of what I have termed rest and division. 



