14 



IXTERCELLULAR SUBSTANCE. 



again. This is repeated two or three times, but finally the farrow 

 becomes permanent, and, deepening into a groove, gradually constricts 



the mass into two. In some cases, before 

 Fig- 8. this process is complete, a second furrow 



appears at right angles to the first, and 

 sometimes even a third, the division 

 being thus into four or eight segments 

 instead of into two only, as previously 

 described in the case of the mammalian 



ovum. 



In the same manner the division of 

 other cells may take place, the nucleus 

 first becoming divided, and a portion of 

 the protoplasm collecting around each 

 half. The two cells thus produced may each undergo a similar change, 

 and in this way cell-multi})lication may be exceedingly rapid. The cells 

 commonly become separated ; in some tissues, however, cartilage, for 

 instance, "they may remain in proximity, producing thus groups of two 

 or four newly-formed cells, which, in the case of that tissue, are at 

 first enclosed in a common cavity of the matrix : hence the process of 

 nnilti[)lication has here been styled " endogenous." It is, however, in 

 all probabilit}^, essentially the same as in the less solid tissues. 



The division of cells is usually into two, as above described, but, as 

 observed by Remak in the frog larva, it may occur into as many as 



five or six. Instances of the 



Fig. S. — Diagram op the Divi- 

 sion OP A Cell. 



N 





Fig. 9. — Multinucleated Cells. 400 Diameters 

 (Kolliker). 



Fig, 9. same kind are also observed 



in the development of pus 

 corpuscles from connective 

 tissue corpuscles, the cells 

 becoming enlarged, and their 

 nuclei multiplied previously 

 to breaking up into pus cor- 

 puscles. Sometimes, however, 

 a multiplication of nuclei 

 within a cell would seem to 

 occur without immediate 

 separation into new cells, as, 

 for instance, in the case of the 

 large flattened multinucleated 

 cells (fig. 9), which are found in the medullary cavities of bone, and 

 in other situations, and which would seem, at least in bone, to fulfil 

 a special function. 



Of cells in their relation to each other. — The cells which com- 

 pose the early eml)ryo have but little connection one with another, the 

 intercellular substance being small in amount, or altogether absent. 

 As growth proceeds, however, they come to present differences in their 

 relations to each other. 



(/. They may remain isolated, as in the instance of the pale corpus- 

 cles of blood, chyle, and lymph. 



&. Tiicy may be united into a continuous tissue by means of a 

 cementing substance : the epithelium and cuticle, the nails and hairs 

 afford instances of this. 



c. Processes from neighbouring cells meet and become united, as is 



