114 PROTECTIVE FEATURES IN YOUNG OF VERTEBRATES. 



and glassy translucency, as in all pelagic animals, protects them, 

 moreover, from sharp-eyed predaceous foes. 



Hosts of the lower animals — starfishes, annelids, molluscs, etc. 

 — are likewise pelagic, and when young possess this translucent 

 character. "Pelagic animals," said the late Professor Moseley, 

 "generally seem to be colourless or specially coloured with a view 

 to protection from enemies both above and below the surface of 

 the water. Probably the blue colour of Ianthina and Velella is 

 protective as resembling that of the ocean water. . . . There 

 are numerous other pelagic animals thus coloured blue for protec- 

 tion, such as the mollusc Glaiicus, Porpita (allied to Velella), and 

 some Salpie in which the nucleus is blue. There are also blue 

 Medusce." While animals, young and adult, vertebrate and 

 invertebrate, may be thus protected by their extraordinary trans 

 parency, which renders them practically invisible in the surface 

 waters, they are frequently armed also with deterrent spines and 

 defensive thorny projections. Many larval fishes are now known 

 to possess parallel structures. The young angler, the gurnard, 

 and other familiar fishes in our own seas have a formidable array 

 of transient spikes and protuberances upon the body. A larval 

 angler, five days after hatching, shows a finger-shaped knob in 

 the middle of the dorsum. It is the rudiment of a larval spine. 

 Two oar-like organs are also rapidly pushed out below and behind 

 the small pectoral fin-pads. They are hardly recognisable as 

 ventral fins, though they really are such. On the fifteenth day 

 no fewer than three formidable spines appear on the back— two of 

 enormous length, just behind the head, curving backward like 

 lengthy tapering whips, while a third erects itself as a blunt pro- 

 tuberance half-way along the dorsum. The head becomes 

 flattened and exhibits angular projections, the gape widens, and 

 the ventral fins now resemble lengthy tentacles hanging below the 

 trunk, and subsequently they become bifurcate and deeply tinted 

 with black. All these spiny projections are supported by strong 

 central rods of cartilage connected with the axial skeleton and 

 limb-girdles. Thus they are somewhat rigid, and impart to the 

 young fish a most formidable and grotesque appearance. Many 

 other curious examples of such structures might be instanced: the 

 ling and rocklings with their enormously long ventral fins, the 

 gurnard and pogge with their huge expanded pectoral fins and 



