PROTECTIVE FEATURES IN YOUNG OF VERTEBRATES. 113 



angler even the tail, in most of our common fishes as slender as 

 the blade of a knife, is rendered thick and club-like. Delicate 

 strands appear to pass across this fluid-filled sub-epidermal space, 

 as in the lamprey, the angler, and other fishes. It is not difficult 

 to surmise that this gelatinous layer around the delicate trunk 

 serves a purpose identical with that of the amnion and other 

 cushion-like coverings in the reptilian, avian, and higher vertebrate 

 embryos. Buffeted about in the surface waters of the sea, or 

 carried hither and thither by strong currents in lakes and rivers, 

 minute larval fishes might suffer severely were it not for these 

 surrounding coats of membrane and abundant fluid. Like the 

 fatty blanket or blubber of the cetacean's skin, these layers pre- 

 serve the larvae from hurtful alterations of temperature. Most of 

 our marine food-fishes, such as the cod, haddock, mackerel, sole, 

 plaice, etc., exhibit " sub-epidermal " enlargements of this char- 

 acter, and over the head-region, where the sensitive brain, the 

 delicate ears, .eyes, and other important organs are located, they 

 serve to shield these parts from the shocks of the surrounding 

 water. The larval sole exhibits curious enlargements in the 

 anterior region, and in the small Irish sole, recently described by 

 an able scientific observer, Mr. E. W. Holt, they have the form 

 of a huge bladder protruding from the forehead. But in the 

 angler {Lophius) these enlargements, as already stated, reach a 

 most extraordinary stage of development. Thus the cavity over 

 the spinal cord and brain, enclosed by the arachnoid sac, probably 

 the " subdural space " of higher forms, is extremely large. It is 

 roofed over by the coloured serous membrane, external to which 

 is a " peri-neural " space limited externally by a delicate mem- 

 brane, the last forming the floor of a third or "sub-epidermal 

 space " proper, common to all young fishes and outwardly limited 

 by the integument. The delicately organised central nervous 

 system is thus shielded from pressure and external agitations by 

 this triple envelope of fluid-filled chambers and protective mem- 

 branes. No doubt these have some interesting phylogenetic 

 meaning, if we could only discover it ; but they may without 

 hesitation be regarded as amongst the most interesting and 

 important protective provisions for securing the welfare of the frail 

 organisms possessing them during larval life. Their minuteness 



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