522 W. B. HARDY. 



of a uniform texture, and behaves towards osmic acid and other 

 stains in a manner closely resembling the muscular elements 

 of the ectoderm. The protoplasm of the expanded end of the 

 cell encloses the following structures. One, rarely two, nuclei, 

 which vary so much in position as to suggest an extreme 

 mobility of the contents of the cell. A varying amount of 

 pigment, dark brown in colour, and disposed in scattered 

 grains near and on the free surface of the cell, but usually in 

 little heaps of grains in the deeper parts. One or more large 

 vacuoles. And, lastly, turbid masses of substance, some of 

 which are certainly the remains of material which has been 

 ingested by the cell, and all of which are in more or less 

 obvious relation to the vacuoles. 



These factors sum up the constituents of the apical cell as 

 usually seen ; but the extent and character of the vacuoles 

 and the turbid masses of enclosed matter vary very much at 

 different periods and in adjacent cells. To this, however, we 

 will return later. 



In the varying position of the nuclei we have some indica- 

 tion of the mobility of the protoplasm of the apical cells ; and 

 this mobility finds further expression in the fact that from the 

 free surface of the cells pseudopodial extensions are pushed 

 out, especially from those cells which are fairly free from 

 enclosed masses (cf. Allmann's * Memoir,' pi. Ivi, fig. 2). 



In the middle tentacular region the endoderm assumes a 

 different character. The goblet-cells disappear, and the pali- 

 sade-cells gradually pass into a shorter and broader type of 

 cell, mostly with only one nucleus. These cells I will call 

 vacuolate cells, adopting the term applied by previous observers 

 to similar cells occurring in Hydra. These cells usually 

 contain numerous round hyaline corpuscles, which vary in 

 their characters but stain always with osmic acid and many 

 aniline dyes (such as methyl blue and green), but typically 

 take no coloration with hsematoxyliu and little or none with 

 carmine stains. These are, without doubt, identical with the 

 sphere-like masses of reserve nutriment described by Miss 

 Greenwood as occurring in the vacuolate cells of Hydra 



