GENERAL BIOLOGY 



IV. STUDY OF PREPARED SECTIONS. 



Examine series of transverse and longitudinal sections of hydra 

 prepared by the paraffin method, and note the large central enteron 

 surrounded by a body wall of two layers of cells. 



1. The ectoderm. Is it of uniform thickness? In it observe: 



(a) Large squarish or conical cells. Do they contain nuclei and 

 vacuoles ? Their basal ends are continued into muscle fibres (Klein- 

 enberg's Fibres) which are mainly longitudinal in direction, and 

 in cross-section appear as a row of refractive dots on the sur- 

 face of the supporting lamella. Over the outer surface of these 

 cells is a thin cuticle. At the foot the ectoderm cells are more 

 columnar and contain granules, (b) Interstitial cells are present 

 over the body and tentacles but absent in the foot; they stain 

 deeply, (c) Nematocysts, abundant in the tentacles, less numerous 

 on the body and absent on the foot. Are they found in the endo- 

 derm? 



2. The supporting lamella. A thin, deeply staining layer be- 

 tween the ectoderm and the endoderm. Is it composed of cells? 



3. The endoderm cells; variable in shape and size. They are 

 of two kinds: (a) Larger cells, irregular in shape and size, con- 

 taining vacuoles, and with the nucleus flattened and near the basal 

 end. In H. viridis the basal part of each cell contains rounded 

 bodies, chloroplastids, coated with chlorophyll. In H. fusca similar 

 bodies are present, "sooty corpuscles," devoid of chlorophyll. The 

 basal ends of these cells are often prolonged into muscular pro- 

 cesses like those of the ectoderm cells, but transverse in direction. 



(b) The smaller secretory cells, pear-shaped and lying between 

 the bases of the larger ones. These last mentioned cells are num- 

 erous in the walls of the hypostome but fewer elsewhere. Their 

 protoplasm is granular and they stain deeper than the larger cells. 



Make a drawing of each section. 



V. STUDY OF ISOLATED CELLS. 



Place living hydra on a slide, draw off the water and cover for 

 a few minutes with a drop of Haller's Fluid. Cover and tap gently 

 upon the cover glass to separate the cells. 



Select and draw good examples of the varieties of cells men- 

 tioned. 



. 

 v * * 



.". 

 ^ 



r , ML is 



[47] 



