112 PROTECTIVE FEATURES IN YOUNG OF VERTEBRATES. 



creatures being prevented by the slippery nature of the enveloping 

 jelly. Toad-spawn does not form irregular masses, which rise from 

 the bottom of the water soon after deposition as in the case of the 

 frog, but appears as gelatinous ropes, very tenacious and many 

 yards long. The newt's eggs are similarly surrounded by a clear 

 fluid contained in a skin or oval capsule, the central vitellus being 

 spherical and buff-coloured. Such coverings of membrane and jelly- 

 like fluid protect the delicate embryo during its early development 

 in various ways, and are cast aside, like the amniotic envelopes, 

 when free life is entered on. A gelatinous coat surrounds the 

 lamprey's ovum, and similar mucous matter forms the huge float- 

 ing egg-ribbons of the angler fish {Lophins). The glassy eggs 

 of the angler are scattered through the glairy mucus, and thus 

 shielded from the shocks of the waves. 



The jelly in fish and amphibian is an oviducal secretion not an 

 essential part of the egg and not a product of the ovary. It is 

 absent from the eggs of many fishes, a great number being simply 

 provided with a thin capsule or vitelline membrane, so called 

 because it arises as a skin or pellicle upon the surface of the yolk, 

 and when hardened forms a resistent shell provided with pores, 

 and in numerous species with knobs, filaments, and other projec- 

 tions. The capsule in the eggs of the hag-fish (Myxine) and 

 other forms is regarded by many authorities as a chorion secreted 

 by the oviduct and not a true vitelline membrane. The germ 

 and yolk do not usually fill the chamber of the egg-capsule com- 

 pletely, and the perivitelline space (Ransom's breathing chamber) 

 is filled with a dilute organic fluid, which forms a protective layer 

 within the capsule. Upon emerging from the egg the larvae of 

 fishes and many other vertebrates are delicate and comparatively 

 defenceless. A larval herring, haddock, or cod is a minute worm- 

 like creature, rarely more than ith of an inch long, with a trans- 

 lucent body, a tapering dagger-shaped tail, blunt head, and with 

 mere rudiments of paired limbs. The skin fits as loosely as 

 Falstaff's tunic upon a lanky starveling, and the space separating 

 the skin from the muscle-masses of the trunk is occupied by 

 a clear serous fluid. In the larval frog and other amphibians 

 this lymphatic layer is present, and in some bony fishes its quan- 

 tity increases to such a degree that the head and trunk are 

 swollen enormously as with some dropsical affection. In the 



