

1891.] Observations on the Gestation of Indian Rays. 207 



rounded extremity. They are with difficulty straightened out from 

 their wavy curl. In stained preparations a dark unbranched line is 

 seen folio wing the sinuosities of the trophonema, nearer to one margin 

 than to the other, and tapering away to nothing at the apex ; it is the 

 rounded thickening formed by the (developing) axial vein which is so 

 conspicuous in the trophonemata of Pteroplatcea. 



A trophonema, lightly stained with borax carmine, mounted in 

 spirit and glycerine, and viewed under a Zeiss D ocular 2 by trans- 

 mitted light, shows a darker and broader median band and two lighter 

 and much narrower marginal bands. In the former the axial vein 

 presents itself as a streak with a pale axis, which transverse sections 

 prove to be the optic expression of the commencing lumen. In each 

 of the latter a large vessel, which in transverse section is seen to be 

 an artery, can readily be made out. By careful focussing, the surface 

 of the broad median band is seen to be covered with a coarse polygonal 

 network, with paler meshes, which correspond to the simple or com- 

 pound duct-openings of subjacent glands; the network, like the 

 surface of the pale marginal bands, is covered continuously with 

 minute flat glassy cells having sharply denned nuclei and distinct 

 limiting membranes. Some preparations suggest that, in tropho- 

 nemata which are less advanced in development than the one under 

 description, this layer of pavement cells may form a continuous 

 investment over the whole trophonema. 



Transverse sections of a trophonema show that the meshes of the 

 polygonal network above referred to coincide with bulb-shaped nests 

 of cells which are the still solid foundations of glands. 



These glands are arranged, as in Pteroplatcea (vide * Roy. Soc. Proc.,' 

 vol. 49, PI. VIII, fig. 5), perpendicular to the surface, side by side, in 

 the substance of the mucosa, but not quite so close together. They 

 are squat bulb-shaped organs, and are often compound, with two, 

 three, or, perhaps, four acini. In consequence of the absence of 

 limiting cell-membranes, the exact arrangement of the gland cells 

 cannot be made out, but the nuclei, which are elongate, are arranged 

 somewhat irregularly in two strata the nuclei of the two strata and 

 of the same stratum overlapping one another ; whence it may be 

 inferred, though no cell-boundaries are traceable, that the gland 

 tissue forms a two-layered stratified columnar epithelium similar to 

 that which is found in many parts of the Mammalian respiratory 

 tract. 



The glands, which, as above stated, are quite solid without any 

 trace of lumen, appear to have originated as ingrowths of the in- 

 different layers of the epithelium alone, the outer layer of flat glassy 

 pavement cells which invests the surface of the trophonema between 

 the glands and at its sides not having been involved in the process. 

 And, from appearances presented by less developed trophonemata, 



