CELL-MEMBRANES. 59 



two adjacent cells is always to be regarded as a derivative of both 

 (p. 16). 



The partitions are often perforated by holes or canals, by 

 means of which a free communication is established between ad- 

 ioining cells. (See Fig. 4.) It has recently been demonstrated 

 that such perforations often give passage to threads of protoplasm 

 connecting the adjacent cell-bodies. The latter, in fact, are 

 seldom or never completely isolated by the partitions which sur- 

 round them. In some tissues the partition-walls may be partly 

 or wholly wanting, the cell-bodies being in immediate contact. 



C 



FIG. 30. Diagram of developing cartilage: ~, single cell surrounded by its membrane or 

 capsule (c 1 ); B, the same cell divided into two, each of which is surrounded by a sec- 

 ondary capsule (c 2 ); in C, the two have divided into four, each surrounded by a tertiary 

 capsule ; the primary and secondary capsules now form the matrix. 



In other cases the cell-bodies are not only in contact, but actually 

 fuse together, so that the whole tissue consists of a continuous 

 mass of protoplasm, in which nuclei are imbedded. In this case 

 the tissue is called a syncytiiim. It is exemplified by ordinary 

 striped muscle, which consists of elongated fibres, each of which 

 contains a number of nuclei and therefore represents a corre- 

 sponding number of cells fused together. 



It often happens, especially in the tissues of animals, that the 

 partition-walls become of great thickness, the membranes fusing 

 more or less completely together to form what is known as the 

 intercellular substance or matrix. The cells then are scattered 



