CELLS. 47 



striated muscular fibres on the other hand, it is evidently the 

 fibrillin or the contents which are contractile, and the sarco- 

 lemma, as an elastic yielding body, only moves with them : 

 the same appears to hold good with the muscular fibre-cells, in 

 which a special membrane cannot be demonstrated.] 



§18. 



Metamorphoses of Cells — Kinds of Cells. — The destination of 

 the cells which are found at an early period in the organism is 

 very various. A very considerable portion of them remain but 

 for a short time in their primitive condition, and subsequently 

 coalesce with others to form the higher elementary parts. 

 Another portion, while they enter into no such combinations, 

 change more or less their previous nature ; as the horny plates 

 of the epidermis and nails. Many cells, lastly, never become 

 metamorphosed at all, but remain as cells, until sooner or 

 later, often not before the decay of the organism, they dis- 

 appear accidentally or typically, as the epithelia, glandular 

 parenchymata, &c. 



The permanent cells may be most conveniently arranged 

 under the following heads : 



1. True cells, which have in no essential respect altered 

 their cellular nature. These occur in the epidermis [stratum 

 Maljnghii) and the epithelia ; in the blood, chyle, lymph ; in 

 the glandular secretions, in the fatty tissue, in the grey nervous 

 substance, the red bone-medulla ; in the glands (liver, spleen, 

 suprarenal capsules, closed glandular follicles), and the carti- 

 lages. According to their form, these cells may be divided 

 into round, discoid, cylindrical, conical with cilia, and stellate ; 

 according to their contents, they may be distinguished as con- 

 taining fat, protein or serum, hsematin, bilin, pepsin, mucus, 

 or pigment ; and as to their modes of occurrence, some are 

 either isolated in fluids or in solid tissues, others are united 

 into a simple cellular parenchyma, while others are conjoined 

 by an intercellular substance of one kind or another. 



2. Metamorphosed cells, which have more or less altered 

 their original structure. To these belong : 



a. The horny scales : flattened, polygonal, or fusiform ; their 

 membrane being fused into one mass with the contents. In the 

 epidermis, the laminated pavement epithelium,the hairs and nails. 



