THE REACTION OF HYDRA TO INANITION. 179 



stumps of tentacles. Our slide shows the tentacular stumps 

 involving but a few sections of the series, thus recording their 

 small size. Hydra-tissue, being digested within the coelenteron, 

 is found in these sections. While within the endoderm's epi- 

 thelio-muscular cells are many nematocysts. 



Another specimen, "369 i," was kept isolated within a 

 hanging drop for three days and examined daily. At the end of 

 this period, it was found to be in a listless condition and to 

 have very short tentacles. This Hydra, in the fixed and sectioned 

 condition, revealed many nematocysts within the coelenteron and 

 food-vacuoles of the epithelio-muscular cells of the endoderm. 



Specimen "380" was isolated in a test tube. This tube was 

 kept partly submerged in the pool from which the Hydra had been 

 taken. Daily inspection revealed that on the seventh day the 

 tentacles were blunt, their ends ragged, no amcebas or other 

 parasites present. The series of sections on our slide 380 shows 

 almost wholly digested hydra-tissue within the ccelenteron, there 

 being left, as yet, naked nuclei, at one side of the dissolving mass, 

 and a cnidoblast, in bad condition, surrounding a "stinging" 

 nematocyst. In addition to this there are many nematocysts in 

 various phases of digestion within endodermal cells. 



These observations indicate that, not only are the protoplasmic 

 constituents of the ingested fragments of tentacles digested and 

 absorbed, but that even the nematocysts are likewise appropri- 

 ated as food. 



The fact that these structures can be digested by Hydra is 

 interesting. Glaser and Sparrow ('09) found that "in the case of 

 peptic digestions, all the tissues except the nematocysts, were 

 dissolved," p. 362. But it has since been observed that parasitic 

 ciliates and amoeba can digest the nematocysts of Hydra. The 

 histology of Microstoma's enteron or "intestine" greatly re- 

 sembles that of Hydra and it does not digest the nematocysts 

 but hands them over for offensive or defensive purposes to the 

 mesenchyme. Hydra's immediate demand, during inanition, is 

 neither defensive nor offensive but nutritional, so it digests 

 the nematocysts. Fig. i shows a nematocyst from which the 

 cnidoblast has already disappeared. Except for the lacking 

 cnidoblast the nematocyst, as it lies within the food vacuole of 



