270 CHAS. W. HARGITT, 



With the approach toward differentiation there occurs a more 

 or less evident cellular change, the cytoplasm concentrating about the 

 nuclei, in cubical blocks, but still without the formation of a cell 

 membrane, which does not appear till sometime later. 



Glandular cells. About this stage in the history of the 

 ectoderm there appear certain cellular elements which are destined 

 to form a conspicuous feature of the later development. On the inner 

 border of the now fairly differentiated ectoderm appear large, oval, 

 more or less vacuolated cells with usually prominent nuclei, and with 

 their long axes parallel with the surface of the embryo. Their cellular 

 cytoplasm is definitely reticular with a more or less granular mass 

 about the nucleus, and in many cases the entire cell highly vacuolated. 

 The fact that these vacuoles remain under the varied phases of 

 staining show that they are probably filled during life with watery 

 cell-sap, or thin mucous. They are in all probability glandular 

 cells, supplying possibly during later embryonic development a dis- 

 gestive ferment which contributes toward the further reduction of the 

 yolk masses and their transformation into available proteids. With 

 the growth of the embryo their position tends toward the surface 

 and with the escape of the embryo they have assumed a position 

 more nearly parallel with that of the ordinary ectoderm cells, or with 

 their long axes at right angles to the surface. This would naturally 

 comport with their now changed function as mucous cells which supply 

 the abundant mucous or slime, so characteristic of planulae of nearly 

 all hydromedusae, and particularly of those of the Eudendridae. These 

 larvae, while quite free, and swimming for a time near the bottom of the 

 aquaria, always leave a trail of slime, which sometimes in small dishes 

 becomes so abundant as to more or less tangle or enmesh them, and 

 also to render difficult their easy separation individually for transfer 

 or for fixation and preservation. 



Figs. 22—30 drawn by aid of the camera will show the several 

 forms and aspects of these cells at various stages of development. 



With the release of the planula from the gonophore and during 

 its free-swimming life these cells become relatively more abundant in 

 the aboral region, which is what might be naturally expected as one 

 considers the secretory function necessary during the later larval life 

 in the fixation of the young polyp and the secretion of the perisarc 

 about its base. I have not undertaken to follow their history during 

 the later development of the hydrauth, nor of course, in the mature 



