SKELETO-TROPHIO TISSUES AND COXAL GLAXDS. 137 



cartilage) is not fibrillar (naonaxial) nor membranous (biaxial). 

 It is block-like, and its cells multiply equally in the three 

 directions corresponding to the axes of a cube (triaxial cell- 

 division). It is not developed under conditions of pressure 

 or tension along constant lines or planes but is subject 

 to a uniform tension or pressure on all sides. This is true 

 even of elastic or reticular cartilage. 



It is extremely difficult to decide whether the word " carti- 

 lage'^ can be properly applied to the entosternite of Limulus. 

 If " cartilage" be defined chemically it certainly is not appro- 

 priate. But is it desirable to define the species of a histological 

 system with reference to chemical characteristics ? How could 

 we thus define " epidermis?'^ Should we not thus be led to 

 separate too widely the chemically- differing gland epithelia ? 

 On the other hand, it is not clear that the word "cartilage" 

 has been used by either anatomists or histologists with any 

 sufficient morphological limitation. So far as mere texture and 

 quality of substance goes, the entosternite of Limulus would 

 be spoken of as cartilaginous. It seems, however, possible to 

 consider the species " cartilage'' as morphologically defined by 

 the isolation of each one of its constituent cells in a firm matrix, 

 and by the triaxial multiplication of those cells, w^hether the 

 matrix be homogeneous or fibrillated (fissured), or penetrated 

 by reticular condensations. In this sense the entosternite of 

 Limulus cannot be said to be " a cartilage," nor, indeed, can the 

 white fibro-cartilage of Vertebrates be properly so called. 



For the present, then, it will be best to speak of the tissue 

 which forms the entosternite of Limulus as a chitinigerous fibro- 

 massive skeletal tissue. The terminology of histology has not 

 really at present a proper name for it, and it would take us too 

 far out of our way on the present occasion to devise a system 

 of nomenclature of skeletal tissues in which this particular 

 variety should find a properly-defined place. 



In Limulus this same tissue is found as the constituent 

 of six small entochondrites, which exist in the successive seg- 

 ments of the mesosoma, placed in the middle line ventrad of 

 the nerve-cords, and giving attachment to muscles. It is also 



