3i6 HYDRA chap. 



remains attached) and a long filament, with three large and several 

 smaller spines or barbs at its proximal end. (Smaller thread-cells, 

 with thicker threads and no spines, are also present'-; some of these 

 have long, spirally coiled threads, others shorter, straight threads. These 

 can be seen better later on. ) 



7. The endoderm, consisting of a single layer of large amoeboid cells, 

 which in H. viridis contain green chromatofhores. Note the currents 

 in the tentacles, which are produced by long vibratile Jlagella present 

 on many of the endoderm cells. 



S. 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 ihe 

 ectoderm and endoderm. Sketch. 



10. Examine a specimen with buds in different stages 01 development, 

 and note as miich as possible of the mode of asexual reproduction by 

 gemmation. Sketch. 



11. If none of your specimens bear sexual organs, try and 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, usually not far below 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 near 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. 



1 1" Place some Hydrje in a watch-glass with a very small amount o 

 water, and when they have expanded, pour quickly over them a warm 

 saturated solution of corrosive sublimate in alcohol. Wash several 

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

 and wash with weak and then with stronger alcohol. Place in"absolute 

 alcohol for a few minutes, and afterwards in turpentine 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 



