10 



C. Place on a glass slip and examine with a high power, noting — 



1. The large ectoderm nenro-muscular cells, with their nuclei, and the processes 



which form the fibrillated layer between the ectoderm and endoderm. 



2. The small interstitial cells lying between the large ectoderm cells. 



3. The threadceUs (nematocysts), some with the thread still coiled up within 



the sac, and others with the thread everted. Observe that some of the 

 threads are short, while others are long, and that some of the long threads 

 have three short barbs at their base. If the threads are not visible, a. 

 drop of acetic acid usually leads to their eversion. 



4. The endoderm cells forming a single layer with delicate processes (ciHa) pro- 



jecting into the body cavity, and with food particles and vacuoles scattered 

 through the protoplasm, and in H. viridis with, in addition, chlorophyll 

 granules. 



5. A testis, which when flattened by pressure on the cover glass, is seen to 



contain ripe or developing spermatozoa. The ripe sperms consist of a 

 head and of a long motile filament, while the developing sperms may either 

 be — (1) in the form of small round granular or hyaline ectoderm cells ; or 

 (2) small oval cells with a process growing out from one end to form 

 the filament. 



6. An ovary which may contain — (a) a number of small round cells; (6), a 



large round nucleated cell, surrounded by small cells ; (c) a ripe ovum, — 

 a large irregular-shaped amoeba-like cell, with a distinct germinal vesicle 

 and a germinal spot ; or (d), an ovum in process of segmentation enclosed 

 in a thick capsule. 



D, Indicate in an ideal transverse section the ectoderm cells with their thread 



cells and processes, the interstitial cells between them, and the endoderm 

 cells, with their cilia, vacuoles and granules lying within the fibrillated layer. 

 Indicate also the various stages seen in the development of the spermatozoa 

 and ova, and a segmented ovum if present, within its capsule. 



Advanced Students should make and examine transverse sections of the body 

 and tentacles of hardened specimens, in order to study and draw the ectoderm and 

 endoderm cells, their various processes, and the nematocysts. 



