Ryder.] 55b [Nov. 1, 



representing a long bone. This deposit is at first thickest around the mid 

 die of tlie long bones for the same reason as that already assigned for the 

 early appearance of calcareous deposits in the middle of the diaphysis, 

 viz., the greater age of this region. 



In calcified bones of Batracliia, Kastschenko has shown that these first 

 homogeneous deposits contain no bone corpuscles, an observation which 

 I have confirmed, while KiJlliker has lately recorded similar facts regard- 

 ing the bones of very young Mammalia, while my own studies in fishes 

 show that there are forms, such as the Lyomeri, which reach even the 

 adult stage without including a single osteoblast in any of their calcified 

 bones. I may further add that embryonic membrane bones of Mammalia, 

 and especially of fishes, at first develop and calcify in the form of abso- 

 lutely homogeneous plates or in reticuli of a dense homogeneous substance 

 allied to collagen. 



Summarizing these results still further, it may be said that : 



1. Tlie indifl'erent intercellular colloid or gelatinoid tissues of inverte- 

 brates and vertebrates have a labor saving as well as a supporting 

 function. 



2. The same may be said of the indifferent or ametabolic vesicular and 

 uotochordal tissues of invertebrates and vertebrates. 



3. The indifferent, ametabolic or passive qualities of both these kinds of 

 tissues apparently leads to the throwing down of homogeneous cuticular 

 deposits upon their surfaces by the surrounding tissues, in much the same 

 way as indifferent foreign bodies are encapsuled by colloid laminated mem- 

 branes, and which may become infiltrated with calcareous matter. 



4. Osseous or calcareous infiltration of gelatinoid or colloid matrices, 

 and of homogeneous reticuli or membranes, always begins in the oldest 

 parts of the same, in conformity with what would be expected of them 

 on a priori grounds and in view of their ametabolic physical properties. 



A homogeneous membrane of collagen may give rise by intercellular 

 extension and deposit to a reticulum consisting of the same substance. 

 This happens in the vertebra? of sharks, where such a reticulum invades in 

 an outward direction the investing rings of cartilage forming the bodies of 

 the vertebnieand calcifies directly without the intermediation of the inva- 

 sive or irruptive processes which accompany the formation of the cancel- 

 lous tissue of the bones of manj^ vertebrates, including Teleosts, Batrachia, 

 Reptilia, Aves, Mammalia. 



The cartilaginous tube investing the notochord in sharks has probably 

 been evolved through a condition which is permanent in Clmnara, where 

 the cartilage at the bases of the neural and luemal arches has begun to 

 irrupt through the outer membrana elasti(?a externa into the here enor- 

 mously thickened fibrous membrana elastica interna. In Teleosts the 

 elastic sheath in many cases seems to calcify and segment directly into the 

 vertebral rings. In other forms the elastica externa is the first to calcify, 

 even long before the cartilage of the vertebral centra. The elastica ex- 

 terna is rudimentary in Aves, Reptilia and Mammalia, and can be seen 



