436 



TEMP. -MAJOR H. M. EVANS ON 



The tissue of the triangle at this stage consists of the fibrous 

 tissue which precedes the formation of bone ; the pigmented layer 

 and the round cells in this way extend over the tissue of the 

 groove, and the actual separation of the spine from the tail is 

 accomplished by a division of the round-celled epithelium, so that 

 when the separation is complete there is a pigment-layer covering 

 the glandular triangle covered with several layers of epithelium^ 

 and a similar pigment-layer with epithelial covering facing it on 

 the doisal surface of the tail, 



Text-fie-ure 5. 



Trygon pastinaca . 



A. Transverse section of spine near base. 



B. Lateral canal and nipple. Canal full. 



C. „ „ „ Canal emptying. 



e.c. Central canal, d.m. dentate margin, f.g. follicles of gland, g.t. glandular tissue. 

 l.h. lacunae of bone. I.e. lateral canal, m.r. median ridge, n.l.c. nipple of 

 lateral canal, s. secretion. 



The pigment-layer may also be observed to dip into the trian- 

 gular area, and carries with it these rounded cells. 



If we now examine more carefully the secreting tissue of the 

 glandular triangle, we notice throughout the length of the 

 groove, but more markedly near its base, two definite rovmded 



