3 io 



ENDOCRANIUM, BRANCHIAL AND NEURAL CARTILAGES. 



for a short time in caustic potash, the perichondrium and muscles are at once 

 dissolved, leaving the cartilage bar clean and free from all other tissues. The 

 cartilage swells and turns yellow and transparent, but otherwise appears to be 

 unchanged. After prolonged boiling it breaks down and disappears. 



Thin sections of the gill bars, boiled in potash till the perichondrium is com- 

 pletely dissolved, show under the microscope irregular crevasses and spaces 

 around the central cell nests, indicating that the clear matrix, or cement, sur- 

 rounding them has been dissolved out. The capsules themselves are swollen, 

 and their walls appear much more distinctly laminated than before. On further 

 boiling, the axial portion of the section drops out, indicating that the nests have 

 been completely isolated; when boiled still longer, the peripheral portion breaks 

 down also. 



FIG. 211. Section of the branchial cartilage, in an adult Limulus, highly magnified, showing a single nest 

 of cartilage cells. The arrangement of the concentric layers of differently colored chondrin indicates the success- 

 ive generations of cartilage cells. Stained in thionin and picric acid. 



When free hand sections of alcoholic material are treated with thionin, 

 complicated color reactions take place that vary with the thinness of the section, 

 strength of the solution, and apparently with the exposure to air and duration of 

 the staining. The reactions may be studied under the microscope in a watch 

 glass. If the stained sections are mounted in glycerine, it will be seen that the 

 lacunae are lined with a finely granular protoplasm, with one or more small nuclei 

 on the periphery. (Fig. 211^ n.) The center is filled with a fluid, containing in 

 some cases coarse granules of a deep reddish-violet, x'\ in others, large spherules 

 of a faint yellow color, x. In most cases the central portion appears to be empty, 

 and if the sections are carelessly handled they may contain large air bubbles. 



The capsules consist of alternating red, or violet, and blue laminae. The red 

 bands vary greatly in thickness and in the intensity of the color in different cap- 

 sules. The innermost one is deep red, with a rough irregular inner surface, the 

 larger protuberances probably marking the beginning of a new partition. Just 



