HISTOLOGY OF HYDRA 



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alveolar walls forming a reticulum of denser substance, which, 

 in the lower moiety of the cell, is drawn out into a network of 

 fibrils which may be traced into connection with the basal 

 contractile fibre. A large nucleus, with a distinct nucleolus 

 (sometimes there are two nucleoli) and a network of very fine 

 chromatin particles, occupies the middle of the cell. The ex- 

 ternal moieties of adjacent cells are fused together by intimate 

 union of their protoplasmic walls, hence it is very difficult to 



Fig. 49. 



Isolated cells from Hydra/usca, A, a group of ectoderm cells from the body 

 wall showing the muscular fibres. .5, an ectoderm cell from the basal disc 

 showing the secretory granules. C, two interstitial cells from the ectoderm. 

 Df an interstitial cell dividing, very highly magnified. J£, an endoderm 

 cell, not very highly vacuolated with muscular process, nucleus, and 

 plastids. J^ and G, two forms of gland cell from the endoderm of the body 

 wall. 



isolate a single cell, and if one is isolated its edges look torn 

 and jagged, as is shown in the outermost cells in fig. 49, A. 



The cells are limited externally by a cuticle which, under the 

 highest powers of the microscope, is seen to contain a number 

 of minute refringent particles. When the animal is fully 

 extended the cuticle forms a continuous even layer over the 

 surface. When it is contracted, and its walls are thrown into 



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