SECT. II.] ENDOGENOUS FORMATION. 1 9 



circumstance that not all the yelk, but, according to the different 

 animals, a smaller or larger portion of it envelops the newly-formed 

 nuclei. When the process of division has attained a certain stage, 

 all the segments become surrounded with membranes, either si- 

 multaneously or in successive layers, and are transformed into true 

 cells ; from which circumstance we arc warranted in classifying 

 endogenous cell-formation. 



I>. The phenomena attending the endogenous formation of cells by 

 division, which is the usual mode of multiplication in cartilage, are 

 the most complex. Cartilage-cells differ, in my opinion, from the 

 great majority of the cells of the higher animals, in having, like 

 vegetable cells, two membranes, an internal delicate proteine mem- 

 brane, the primordial utricle, and an external firm capsule, analo- 

 gous to the cellulose covering of plants, the latter of which is, as in 

 plants, a secondary formation, an excretion of the former. Where 

 cartilage-cells multiply, the first thing observable is a division 

 of the nucleus into two; then the nuclei separate from one 

 another, and a partition, as it were, passes in between them, upon 

 which the mother cell divides into two completely separated spaces, 

 each of which embraces one nucleus and the one-half of the con- 

 tents of the cell. Subsequently two complete secondary cells 

 generally become distinct within the mother-cell and entirely fill 

 it up, proving that the partition is, properly, double from the 

 commencement. The formation of the partition of the secondary 

 cells is, perhaps, to be understood as being effected in the same 

 manner as in plants : it being as- 

 sumed that, the primordial utricle 

 becomes constricted and ulti- 

 mately divides. Now, in cartilage, 

 the above-mentioned process is 

 repeated, as a rule, many times 

 with great regularity, and in such 

 a manner that the secondary 

 cells, after their formation, 



fivsf sppvpfn pvtpnnl pov+iloo-p Cartilage cells of a full-grown Tadpole, semi- 

 insi hixitic c ail nidi Cdiuuigt diagramnia tical figure. I . A mother cell, whose 



Tnpmhi"inr>« tvLIpIi nnifn with primordial utricle is in the act of dividing a. its 



mtmuidiiLJs, HiiiLii umu, \\ till j^ secondary membrane or cartilage capsule. 



thnsp r»f thpiv rnnflirr roll find nt *■ Primordial utricle, enclosing the cell contents 

 uiuhu 01 uu.11 mouu.1 an, <iiiu di with the nucleus, c. Place where it is constricted 



the same time form a partition ^ftgg>- w] with two generations, d. outer 

 between them,— and then divide ccl1 « iembra ?«! f ^E?55!J£i'«f ?w P n™ U 



' membranes of the cartilage capsules of the secon- 



ailCW (Fig. 2). Meanwhile, the tary mother cells enctosed oy th^em, wh^, with 



\ a / f_ t form a double partition through the duet mo- 



Cartilage membranes of the mo- thercell. g.g. Secondary cells. 



thcr cells usually continue to exist for some time longer, but 



c 2 



