680 PROFESSOR W. C. M'INTOSH AND MR E. E. PRINCE ON 



soft and pliant, and may remain so even after deposition, as we find to be the case, 

 notably in the thick capsules of Gastrosteus spinachia and Cottus. These ova, for some 

 time after deposition, are soft and yielding, possessing, as Prof. Allen Thomson (No. 153) 

 states, in the fresh-water congener of the former, " so little elasticity that it usually 

 retains dimples or impressions made upon it from without." In this connection it may 

 be mentioned that the so-called outer laj^er in Clupea harengus is slightly facetted (No. 

 87, p. 177), this being due, doubtless, to the impress of the follicle-cells before the egg is 

 extruded — a suggestion which may also be applied to the similar appearance in the case 

 of Perca (No. Ill, p. 187). The zona radiata, as its name implies, has a characteristic 

 radiate structure in many Teleosteans. The real nature of the striation so visible in section 

 has been much disputed, and there is little unanimity of opinion in regard to it. In 

 many species this feature has not yet been made out, e.g., in a number of familiar 

 Gadoids, viz., G. merlangus, G. ceglejinus, G. luscus, Molva vulgaris, and some of the 

 Pleuronectidse, such as P. fiesus and P. limanda. The capsule in the familiar 

 Pleuronectid, Pleuronectes platessa, again, is very distinctly punctured (PI. I. fig. 20). 

 Cunningham has recently mentioned that the zona radiata of the cod usually described as 

 not punctured (vide Ryder. No. 141, p. 457), exhibits pore-canals, but he does not describe 

 them in the ovum of Trigla gurnardus ; yet the latter, so far as our experience goes, 

 shows them much more distinctly than those of the cod ; indeed, we have not yet 

 satisfied ourselves concerning the latter. In the ovum of Trigla one of us has demon- 

 strated that the whole surface of the capsule is minutely and faintly dotted (PI. I. fig. 

 19). This punctate appearance is especially distinct after the escape of the embryo. 

 The capsule of this form in the unimpregnated condition shows numerous wrinkles — the 

 yolk occupying a comparatively small area, so that a large perivitelline space exists, 

 which, however, diminishes after fertilisation, until the vitelline globe almost fills the 

 capsule, which at the same time becomes less distinctly wrinkled. The corrugation of the 

 zona radiata is, however, a characteristic feature, and exists in all the eggs of this species. 

 The zona is firm and elastic to a remarkable degree for a pelagic form, and its unevenness 

 causes some obscurity — only a faint line of dots being as a rule visible along the ridge 

 which happens to come into focus under the microscope. In one instance the zona 

 presented a series of scale-like markings or areolae (PI. I. fig. 16), probably due to an 

 unusual or morbid condition in connection with the follicular epithelium. The normal 

 wrinkles (seen best in T. gurnardus) also occur in the lemon-dab (PI. I. fig. 18); and 

 Ryder speaks of these in G. morrhua as fine lines crossing each other at definite angles. 

 Such lines, however, are less visible in eggs which are healthy and perfectly mature. 

 The typical zona radiata exhibits, as Von Baer discovered in Cyprinoids, fine striations 

 perpendicular to the superficies of the yolk, and Carl Vogt described at greater length 

 the same feature in the Salmonidse (No. 155, p. 7) ; while Reichert noted it in the ova 

 of Tinea vxdgaris and Leuciscus erytlirophtlialmus, and Leydig in Gobius jluviatilis. 



Are these strise really canals, or merely fine fibrillations, such as we find in the 

 transient zona radiata of the fowl under a high power ? In either case a punctured or 



