DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 683 



is crenate and the sides are furrowed. In the pike Ransom describes the micropyle as 

 trumpet-shaped, and projecting slightly from the surface of the capsule (No. 127, pi. xvi. 

 fig. 25, a) ; while in the minnow, too, the margin is raised around the outer opening of 

 the funnel (Ibid., p. 456). Striae are occasionally seen in certain pelagic forms, e.g., in 

 Trigla gurnardus and Gadus ceglefinus, but the margin of the crater is usually sharply 

 marked, and the aperture itself very clearly defined without radial markings. When viewed 

 in " full face," the funnel seems larger than it really is on account of the torsion, so to 

 speak, of the zona radiata, which appears as if bent in to form the orifice, a feature Andre 

 particularly points out (No. 4, p. 199), and to which we have made reference above. 



The micropyle thus varies in appearance. Usually the external opening is the larger ; 

 but in some cases this is reversed, a large gaping internal opening being present (vide 

 fig. of ovum of G. ceglefinus, PI. I. fig. 14), while the external orifice is small. The 

 striations above mentioned are also visible in this case — the whole peri-micropylar region 

 being granular, while the granules have a tendency to range themselves in radial lines. 

 Near the micropyle in some examples an accessory structure is present, due apparently 

 to a granular protrusion of the zona (PL I. figs. 11 and 15). In this and other cases 

 the micropyle was distant from the germinal area. Fertilisation in pelagic eggs does not 

 produce any marked change in the micropyle, certainly none like that described by 

 Ransom, and just mentioned. In one instance, beside the micropyle proper, was a 

 depression plugged by an ovoid granular structure, while a large group of " oleaginous " 

 spheres lay upon the yolk near the micropyle (PL I. fig. 17). 



Origin, Position, and Function of the Micropyle. — The mode of origin of the 

 Teleostean micropyle is unknown. When first observed in the mature ovum it presents 

 the features maintained throughout the subsequent history of the egg. Leydig describes 

 (No. 97, p. 376, fig. 6) the earliest ovarian egg of Trigla hirundo as somewhat pyriform 

 and stipitate, recalling, in fact, the stalked ovum of Unio, in which the micropyle marks 

 the pedicular point of attachment by which the egg adheres to the ovarian capsule, as 

 Carus was the first to note. Such an interpretation of the micropyle, as the cicatricule 

 left by a pedicle, cannot in the case of the osseous fishes be adopted, and we are still 

 left in doubt as to the way in which the aperture arises. 



It is interesting to observe that in many forms the position of the micropyle is 

 constant, and corresponds to the germinal pole, where the embryonic area is formed, 

 as, indeed, Ransom found in Gastrosteus. In Perca, however, the aperture is turned 

 towards the inside of the egg-tube — the ova being fixed in a cylindrical mass, so that the 

 possibility of the micropyle being blocked up by adjacent ova is obviated (No. 127, p. 456). 

 Gerbe similarly says, " that the micropyle plays an important part, as the disc always 

 collects near the place occupied by it" (No. 57, p. 330). Neither Ransom nor Gerbe 

 examined pelagic ova ; but from the later observations of Ewart and Brook, it would 

 appear that in floating eggs the micropyle is always found in the lower hemisphere 

 (No. 55, p. 55). This position is, of course, the reverse of that in stationary demersal ova, 

 in which a preformed disc is commonly found in the upper (animal) segment ; whereas in 



