CCELENTERATA 175 



[A whole animal stained and mounted may be studied profitably in comparison 

 with the preceding.] 



4. Histology from Sections. If the teacher is not equipped for imbedding and 

 sectioning objects, and desires to carry this work further, stained and mounted 

 sections of Hydras and most of the other prepared sections suggested in this book 

 can be secured for a reasonable sum by applying to any of the large laboratories. 

 By comparison of longitudinal and transverse sections verify your observations 

 concerning the extent of ectoderm and entoderm. What occurs between the 

 layers? Study the shape and arrangement of the cells in both layers. Compare as 

 to size. What is the relation of the nettle cells to the other ectodermal cells? 



5. Histology from Maceration Preparations. Place a specimen in a watch 

 glass, and draw away some of the water with a pipette. When the Hydra is well 

 extended, pour over it an aqueous solution of hot corrosive sublimate. Rinse 

 and place in Muller's fluid or 15% alcohol for 24 hours. Take a portion of the 

 body and place on a slide in a drop of glycerine and water. Cover, and tap the 

 cover-glass very gently with a needle. The cells thus become separated, and 

 their shape may more readily be seen. Instructions for staining may be found in 

 texts on histology. 



Study the nettle cells, the ectodermal cells, the entoderm, and the gland cells 

 of the foot and gullet. 



218. For comparison with Hydra the teacher should secure some alcoholic 

 material of some of the marine hydroids, as Pennaria, Obelia or Campanularia. A 

 few slides should be secured bearing whole mounts and sections properly stained. 



The following points should be studied briefly: Relation between individuals 

 in the colonies, branching. What classes of individuals are discoverable, i. e., 

 how do the different branches end? Is there any covering to the softer portions? 

 Tentacles; are they present? If so, what is their arrangement? Hypostome? 

 Mouth? Is there a gastro-vascular cavity? Ectoderm? Entoderm? Call 

 attention to polymorphism among the polyps or zooids. 



219. Metridium (Sea-anemone). If lack of appropriations will not allow the 

 purchase of sufficient material for class work, the teacher should have at least a 

 few well-hardened and preserved specimens of sea-anemone. From these should 

 be made a series of cross sections from various parts of the body, with a thickness 

 of one-eighth to one-fourth inch. These sections may be fastened to cards or to 

 plates of mica by thread or fine wire and kept in preserving fluid. One specimen 

 should be split lengthwise, and one left whole. Four or five specimens could thus 

 be used from year to year until more abundant supplies are obtained. 



The following studies should be made. Make drawings to illustrate all points 

 made out. 



1. General Form. 



Base, or aboral disc (the end attached during life). 

 Column. 



Oral disc: zone of tentacles; intermediate zone; lip-zone; mouth; siphono- 

 glyphs (grooves in the angles of the mouth), number? 



2. Transverse Sections. 

 Body wall. 



Esophagus; does it appear in all the sections? Siphonoglyphs? 

 Mesenteries. How is the esophagus held in position? What differences 



