Chap. XVIII.] 



THE HYDRA. 



337 



delicate muscle processes (m. p.], which come into close relation 

 with the thin supporting lamella (s. /.), a portion of which 

 adheres to one of the fibres in C. 2. In the interstices between 

 the neuro-muscular cells, especially in the deeper part of the 

 ectoderm, there is an interstitial tissue (int.), composed of small 



D. 



FIG. 100. HYDRA HISTOLOGY. 



A. Diagrammatic longitudinal section through a part of the body-wall. 

 ec. Ectoderm, en. Endoderm. chl. Chlorophyll corpuscles, ci. Cilium. 

 int. Interstitial cells, m. p. Muscle processes, nc. Nucleus, n. m. Neuro- 

 muscular cell. ps. Pseudopodial process, s. I. Supporting lamella, vac. 

 Vacuole. (The regularity of the ectoderm is diagrammatic). 



B. Interstitial cells. ne. Nematocysts. E. Chlorophyll corpuscle. 



C. Neuro-muscular cells. s. ?. Sup- F. Thread-cells (nematocysts). 



porting lamella. G. Spermatozoon. 



D. Endoderm cell. H. Ovum. 



cells, some of which are shown at B. In the patch of cells at 4 

 the boundaries (after osmic) could not be made out. The 

 interstitial cells are absent in the foot. 



Within these interstitial cells are developed the curious 

 organs known as thread-cells or nematocysts. When the tentacle 

 of a living hydra is examined under a high power, long fine 

 22 



