58 HISTOLOGY 



The important feature of this cell is the distribution of its periph- 

 eral cytoplasm, which is drawn out into fine -branching processes that 

 radiate from the central mass. The processes arrive at a common 

 boundary which lies concentrically about and at some distance from the 

 main cytoplasmic mass, making this its center in preference to the 

 nucleus. The processes expand their ends on this boundary, joining 

 with the expanded ends of the other processes. The outer cytoplasmic 

 boundary, so formed, is a very thin shell or hollow sphere sometimes a 

 little irregular in shape, and it is about this shell of cytoplasm and by its 

 agency that the rigid supporting material of the tissue is formed. The 

 amount and arrangement of this substance, which is homogeneous and 

 darkly staining, is determined by the mechanical requirements to be met 

 at this point. Figure 59 shows a group of three of these cells where 

 the supporting substance is not as great in amount or as specialized in 

 arrangement as in the second and third orders of LEIDIG'S cells. 



The peculiar arrangement of the cytoplasm, in threads radiating from 

 the central mass and ending in the peripheral boundary, results in a cell 

 which is not filled by its cytoplasm. This is explained when one realizes 

 what a large and unwieldy cell would result if the cytoplasm should fill 

 the cell entirely. The amount of cytoplasm would be excessive, and life 

 could not be supported in the tissue. This peculiar distribution of a 

 smaller amount fulfills all requirements. 



A body of such cells is a tissue admirably adapted to its use. The 

 compact mass of such rigid shells forms a framework which possesses 

 sufficient rigidity to protect the delicate organs which it surrounds from 

 impact and shearing strains imposed by the heavier surrounding organs. 



The renewal of this tissue is easily seen, especially in the lobsters 

 that are about to cast off their old shell or have just done so, as in the 

 specimen used in this demonstration. The nucleus divides by amitotic 

 division and the two daughter nuclei move to opposite sides of the cy- 

 toplasmic body. A line of separation then appears, passing through the 

 cytoplasmic body and extending from periphery to periphery of the cell. 

 The resulting daughter masses of cytoplasm then move apart. They 

 carry their nuclei on the side farthest from the line of division. The 

 specific connective substance of the cell is then laid down in the dividing 

 septum, which thus becomes a new side to each of the daughter cells (see 

 Fig. 59). It is of interest to note that, during multiplication, these cells 

 lose no part of their functional power, but continue to function as con- 

 nective-tissue elements. 



We shall next, in pursuance of this idea, study the cells in the growing 

 root-tip of a plant, selecting that of the chestnut for the purpose. 



In plants, nearly every cell in the organism is, in addition to what other 

 features it may possess, a rigid connective-tissue cell. This is almost 



