DEVELOPMENT AND LIFE-HISTOEIES OF TELEOSTEAN FISHES. 687 



the transformed substance of the cortex is difficult, if not impossible, to separate from the 

 protoplasm of the germ proper, yet the yolk in the main is neither concerned in the 

 cleavage of the germ proper, nor actively contributes to the increase of the embryonic 

 tissues. In the Gadoids and other forms no vitelline circulation is established, and the 

 absorption of the yolk is a slow and circuitous process.* 



Oleaginous and other Globules. — One of us has already published an account of 

 these bodies, which form a striking feature in the yolk of many Teleostean ova 

 (No. 125). The following remarks refer mainly to T. gurnardus, and they still further 

 explain certain statements in the paper referred to. 



In the ripe ovum of the gurnard the globule (PI. V. fig. 5, og) is of a dull pinkish 

 hue under a lens, while by transmitted light it exhibits a brownish yellow or pale salmon- 

 tint. It is enveloped by a protoplasmic pellicle which sometimes appears incomplete, 

 and forms an equatorial line, with pale pinkish vesicles studded along its border. 

 Unlike those forms in which the globule is imbedded in a definite pocket {e.g., Motella), 

 the globule in the gurnard, as also in Cyclopterus and Cottus (PI. I. figs. 2, 3), is most 

 mobile, and can be made to pass under the disc when the latter is uppermost. On 

 rolling the egg the globule emerges from beneath the disc, and is liberated with a bound 

 at the edge of the rim. Moreover, in passing round it flattens out, and again contracts 

 its diameter, or rather resumes its more spherical form. At times the globule appears to 

 ascend directly through the yolk, though this may be a deceptive appearance, for 

 Ransom found in the very mobile globules of Gastrosteus, that while the}' passed freely 

 through the yolk, they could not be made to go "through its centre to get to the 

 uppermost segments when the egg is rolled round ; in doing so the drops often separate 

 to unite again" (No. 127, p. 436). Ransom accounted for this by the greater density of the 

 central yolk-substance. The passage of the globule under the rim is well seen in the egg 

 of the gurnard when the germ has extended as far as the equator. In certain morbid con- 

 ditions the exact relations of the globule during its movements can be readily determined. 

 Thus the globule is often firmly fixed in the dead egg between the opaque blastoderm and 

 the yolk, or the globule is seen at the side, and cannot be made to pass beneath the disc, 

 possibly on account of the doubling of the edge of the disc, or because the investment of 

 the globule and the periblast have become dense and rigid. During the earlier morbid 

 stages, however, the globule is observed to pass beneath the somewhat opaque disc, and in 

 certain abnormal cases, from pathological change, the globule rolls external to the disc. 



From the above observations it is evident that Mr Cunningham's view (No. 48, p. 6; 

 also PI. II. fig. 19) that the globule moves in the perivitelline space — that is, between the 

 yolk and the zona radiata — is not borne out, since in experiments, such as the above, it 

 passes between the disc and the yolk, and never passes through the protoplasmic cortex 

 of the latter, save in rare morbid examples. In those eggs in which the rim has still a 

 short distance to traverse the globule continues freely movable, and its surface next 

 the yolk often presents a series of small globules and a single large central one. The 

 * Vide " Significance of the Yolk in the Eggs of Osseous Fishes," E. E. Prince, Ann. Nat. Hist, July 1887. 



