64 



Mr. T. J. Parker. 



[Dee, 18, 



osmic acid specimens. Such preparations quite lead one to think 

 that the endoderm is ciliated throughout ; in the sections particularly, 

 (fig. 3), cell after cell is seen bearing one, two, or three cilia. These 

 latter are of great length, in fact nearly or quite as long as the cells to 

 which they are attached ; in some cases indeed, they are longer, as, 

 for instance in the cell to the right in fig. 6. I have never seen any- 

 thing like a " collar " at the base of any of the cilia. 



The amoeboid character of the endoderm cells, as seen in sections 

 or teased fragments of the living animal, is a well-known fact ; but 

 the extent and activity of the amoeboid movements during life has 

 not been sufficiently insisted on. In sections of picric acid or 

 ammonic bichromate specimens, large rounded pseudopodia are seen 

 to be given off: from the cells into the digestive cavity, sometimes to 

 such an extent as completely to obliterate the latter. The length of 

 the cells may, therefore, vary almost indefinitely ; they may be but little 

 longer than the ectoderm cells (fig. 3), or may be two or three times 

 as long (fig. 1). This variation in the size of the endoderm cells, and 

 the consequent variation in the diameter of the digestive cavity, is 

 very marked in my series of sections, nearly all of which are taken from 

 large specimens,* killed in a state of half-extension. When the endo- 

 derm cells are fully extended, it is almost impossible to obtain them 

 complete by teasing. They nearly always break across, and can only 

 be obtained in a fragmentary condition. 



A very noticeable point about the endoderm cells is the presence 

 in their protoplasm, especially towards the far end, of dark-coloured 

 irregular granules, of various sizes. It has been suggested that these 

 are products of excretion; Kleinenberg makes the important observa- 

 tion that their number varies with the state of nutrition of the animal. 



I am convinced that these bodies are food particles, taken into the 

 protoplasm of the cells, from the partially disintegrated bodies of 

 the Entomostraca in the digestive cavity. They are of quite the 

 same nature as the contents of the alimentary canal in many of the 

 common Gladocera and Copepoda; they occur chiefly in the free 

 end of the cell, and in some cases they have all the appearance 

 of being half in and half out of the protoplasm. (See fig. 5.) The 

 particles of the more transparent parts of the body of the Crustaceans 

 will naturally not be so evident in the cell protoplasm ; even these, 

 however, can be made out in a Hydra in full digestion, when the 

 endoderm cells of the distal or gastric region are completely crammed 

 with transparent spheroids. 



The clearest case of ingestion of solid particles is that shown in 

 fig. 1, d, when a diatom is seen to be completely imbedded in the 

 protoplasm of a cell. 



If this explanation of the dark granules is the correct ODe, Hydra 

 * Supplied by Mr. Bolton, of Birmingham. 



