THE SHAD'S ANNUAL PILGRIMAGE. 819 



therefore subjected to great variations of pressure, not unlikely 

 at times approaching half a ton to the square inch. At its migra- 

 tory period the shad rises to the surface from the deep, and the 

 sudden change of pressure thereby occasioned would do great vio- 

 lence to its bodily structure but for an apparent special provision 

 of Nature, to be later explained. 



In the marine profound there are fishes in abundant variety 

 that exist at depths of several miles, and perhaps also in its neth- 

 ermost and as yet unknown deeps. Many of these fish seem to 

 be limited to certain oceanic strata to which their organization 

 may be specially adapted and to no other. From time immemo- 

 rial finny creatures of soft and flufiiy substance and distorted 

 shape have been found floating, sonietimes dead, sometimes bare- 

 ly living, upon the surface of the sea ; but, until the explorations 

 of the Challenger afforded the solution, their nature and origin 

 remained a mystery. The fish then drawn up from the far deep 

 presented upon emergence the same bloated and unsubstantial 

 appearance, which, by the scientists of that famous expedition, 

 was ascribed to the expansion of the contained gases incident to 

 the sudden release of enormous pressure. This expansion had so 

 ruptured or puffed out the tissues of the creature that its entire 

 semblance was without doubt radically altered, the puffy and 

 loosely coherent mass of flesh having originally been a firm and 

 compact substance. Fish of such localized habitat, if venturing 

 too far above their proper stratum, would, despite their utmost 

 effort, be buoyed to the surface by the constantly enlarging vol- 

 ume of the imprisoned gases, dilating measurably with the dimi- 

 nution of the weight or depth of the overlying water, and to such 

 mischances is due the occasional appearance of these forlorn 

 castaways upon the wide bosom of the deep. 



Against such injury or inconvenience the shad, in common 

 with its congeners, is seemingly secured by an anatomical pecul- 

 iarity not as yet fully understood, but believed to be a distinctive 

 adaptation of Nature. In the shad's head there appear a number 

 of tubes presumed to exist for the introduction into the blood and 

 system generally of a sufliciency of water, which fluid may be 

 absorbed or extruded with increase or with diminution of pres- 

 sure, and the tissues become thus adjusted to the varying strain.. 

 This presumptive function does not, of course, admit of experi- 

 mental observation, and in the absence of such demonstration 

 the mode of operation and, indeed, even the purpose of the singu- 

 lar tubes must to some extent remain a subject of speculation. 



Of all our marine food fish shad may be said to be the most 

 popular ; as an edible and as a delicacy it appears upon the table 

 of both the poor and the rich, being equally esteemed by the epi- 

 curean as well as by the unpampered palate. The Chinese have 



