THE MICROSCOPE IN ANIMAL HISTOLOGY. 193 



as basement-membranes, supporting layers or investments 

 for epithelial structures, blood, lymph, muscle, and nerves,. 

 It includes ordinary connective tissue (white and yellow 

 fibrous tissues), cartilage, bone, corneal tissue, dentine,, 

 and fatty tissue. 



Most of the difficulty found in the consideration of 

 these tissues arises from discussions relative to the inter- 

 cellular substance. Max Schultze and Beale agree in re^ 

 garding it to originate from the protoplasm or bioplasm 

 of cells. 



The cells are, according to Frey, originally spheroidal, 

 with vesicular nuclei, and between them is an albuminous 

 intercellular substance a product of the cells, or trans- 

 formed cells which usually undergoes fibrillation, while 

 the cells become stunted, or develop into spindle-shaped 

 or stellate elements. Calcification of the intercellular sub- 

 stance occurs in some of these tissues, as bone and dentine. 



The cells of connective tissue present many varieties. 

 Eecklinghausen first observed migrating lymphoid cells 

 or bioplasts in the cornea of the eye, the tail of the tad- 

 pole, the peritoneum, and in various other places. The- 

 exit of white corpuscles from the vascular walls renders 

 it probable that these amoeboid cells originate in the blood. 

 Granular cells, of various forms rounded, fusiform, and 

 stellate are also observed. Some of the stellate cells 

 give off anastomosing branches. Pigment cells, filled with 

 granular pigment, are also met with (Plate XIX, Fig. 

 145). 



In its earliest stages, connective tissue consists of closely- 

 compressed cells, but in the adult two principal forms 

 have been distinguished ; first, those networks and trabec- 

 ulse, developed from cells, which do not yield gelatin on 

 boiling, and, secondly, fibrillar connective tissue composed 

 of a gelatin-yielding substance. Of the first kind we notice 

 the following varieties : 



1. Independent masses of gelatinous or mucous tissue, 



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