CELLS. 25 



transversely striated muscular fibres ; and in minute gland- 

 tubes. 



Nuclei are most commonly oval or round, and do not 

 generally conform themselves to the diverse shapes which 

 the cells assume; they are altogether less variable ele- 

 ments, even in regard to size, than the cells are, of which 

 fact one may see a good example in the uniformity of the 

 nuclei in cells so multiform as those of epithelium. But 

 sometimes they appear to be developed into filaments, 

 elongating themselves and becoming solid, and uniting 

 end to end for greater length, or by lateral branches to 

 form a network. So, according to Henle, are formed the 

 filaments of the striated and fenestrated coats of arteries ; 

 and, according to Beale, the so-called connective tissue cor- 

 puscles are to be considered branched nuclei, formed of 

 protoplasm or germinal matter. 



3. Cells. The word " cell " of course implies strictly a 

 hollow body, and the term was a sufficiently good one 

 when all so-called cells were considered to be small bags 

 with a membranous envelope, and more or less liquid 

 contents. Many bodies, however, which are still called 

 cells do not answer to this description, and the term, there- 

 fore, if taken in its literal signification, is very apt to lead 

 astray, and, indeed, very frequently does so. It is too 

 widely used, however, to be given up, at least for the 

 present, and we must therefore consider the term to indi- 

 cate, either a membranous closed bag with more or less liquid 

 contents, and almost always a nucleus ; or a small semi- 

 solid mass of protoplasm, with no more definite boundary- 

 wall than such as has been formed by a condensation of its 

 outer layers, but with, most commonly, a small granular 

 substance in the centre, called, as in the first place, a 

 nucleus. In both cases the nucleus may contain a nucleolus. 

 Fat cells (fig. 1 1 ) are examples of the first kind of cells ; 

 white blood-corpuscles (fig. 20) of the second. 



The cell- wall, when there is one, never presents any 



