30 



INTRODUCTION TO CYTOLOGY 



A-D) typically possesses a single unbranched prolongation (axon) and 

 one or more others (dendrites) which often become very elaborately 

 branched, especially in the ganglion cells of the spinal cord and brain. 

 The cytoplasm of the nerve cell contains fine fibrils, and also granules 

 of chromatic "Nissl substance." Cells specialized in connection with 

 motility. such as spermatozoa (Fig. 103) and the cells of certain epithelial 

 tissues (Fig. 36), show complex structural modifications not only in the 

 flagelke, cilia, and cirri which they bear (p. 45), but also in the other 

 cell organs with which the activities of these motile structures are closely 



Fia. 7. ParamcBcium caudatum. Semidiagrammatic figure showing principal parts. 

 C. V., contractile vacuoles. T, trichocyst. N, n, mega- and micronuclei. P, peri- 

 stomial groove. M, mouth. O, oesophagus, with undulating membrane, U. M. F. V., 

 food vacuoles. (After Lang.) ' 



connected. (See Chapter IV.) Secretory cells are often distinguishable 

 not only by the accumulations of secretion products in their cytoplasm, 

 but also by the peculiar forms assumed by their nuclei (Fig. 17, A, C). 

 The cells of connective tissue (Fig. 6. A) form many long interlacing pro- 

 cesses and lie in a supporting matrix which represents their secretions. 

 Cartilage and bone cells (Fig. 6, B} are likewise imbedded in their secre- 

 tions, which are here produced in relatively enormous amounts and, where 

 present, constitute the main supporting framework of the body. 



We thus see that the life of the complex multicellular organism is 

 dependent upon the correlated activities of a multitude of cells per- 

 forming many diverse special functions. It is a remarkable fact, that 



