324 HYDRA CHAP. 



tf (p. 304). Note the currents in the tentacle?, which 

 are produced by long vibratile flagella present on many of 

 the endoderm-cells. 



8. The thin transparent supporting lamella. Sketch. 



9. Treat a specimen with methyl-green. A slight pressure 

 on the cover-glass will crush the animal, and render the 

 interstitial cells and thread -cells especially distinct. Note 

 also other isolated cells of the ectoderm and endoderm. 

 Sketch. 



10. Examine a specimen with buds in different stages of 

 development, and note as much as possible of the mode of 

 asexual reproduction by gemmation. Sketch. 



11. If none of your specimens bears sexual organs, 

 try to procure a mounted preparation which shows them, 

 and examine first with the low, and then the high power. 

 Note (a) the spermaries several conical swellings near the 

 bases of the tentacles ; they are covered with large ectoderm- 

 cells, and contain numerous interstitial cells, each of which 

 eventually gives rise to a sperm with a " head " and vibratile 

 " tail." These are discharged at the apex of the cone, 

 which when ripe may be ruptured by a slight pressure on 

 the cover-glass, (b) The ovaries (sometimes only one), 

 generally situated nearer the proximal end of the body. 

 They are larger than the spermaries and more spherical, 

 but at first have a similar structure. When ripe a single 

 ovum is found in each. Sketch. 



Place some Hydras in a watch-glass with a very small 

 amount of water, and when they have expanded, pour 

 quickly over them a warm saturated solution of corrosive 

 sublimate in alcohol or water. Wash several times with 

 weak alcohol, stain for a few minutes with borax-carmine 

 or hoematoxylin, and wash with weak and then with stronger 

 alcohol. Place in absolute alcohol for a few minutes, and 

 afterwards in turpentine, xylol, or oil of cloves ; mount in 

 balsam. Work through 5 8 again, noting especially 

 the characters of the various cells and their nuclei, as well 

 as 



12. The contractile processes coming off from the inner 

 ends of the large ectoderm-cells (Fig. 76, C). These extend 

 longitudinally, and lie against the outer surface of the 

 supporting lamella. Sketch. 



Examine transverse sections through the body or 

 tentacles (Fig. 76, B) prepared as directed on p. 136, after 

 killing and fixing the specimens as above. Work through 



