CURIOUS PROTECTIVE FEATURES IN 

 THE YOUNG OF VERTEBRATES. 



Bv Edward E. Prince, B.A., F.L.S., &c, 



Professor of Zoology in St. Mungo's College, Glasgo~cV. 

 (Read 6th April, 1892.) 



The great Karl Ernst von Baer was wont to gather around him 

 successive bands of Konigsberg students at the commencement of 

 their professional course, and, holding in his hand a fowl's egg 

 about the fifth day of incubation, he skilfully removed a lid-like 

 portion of the shell in order to expose to their wondering eyes its 

 strange contents. They beheld, as though modelled in miniature, 

 the living chick upon its bed of yellow yolk, with the head dispro- 

 portionately large and rounded, with fleshy stumps for wings, and 

 with developing legs curled up beneath the naked trunk. Von 

 Baer pointed out to them, as the embryonic heart, the pulsating 

 bag beneath the throat, through the transparent walls of which the 

 red blood was seen passing by in quick convulsive motions; he 

 bade them note the curious clefts in the gullet, the "visceral 

 slits," and, above all, drew attention to the sheets of thin mem- 

 brane, full of fluid, like transparent water-cushions surrounding 

 the immature bird. With the entrance of cold air into the warm 

 chamber of the egg the body of the chick was seen to move very 

 obviously, for the movements, as well as the whole general struc- 

 ture, of the embryo, could be seen in the midst of its strange 

 envelopes of membrane and clear fluid. 



The curious enveloping structures present in the young 

 stages of all the higher animals have been variously interpreted. 

 Some regard them as having arisen when the yolk-matter of 

 the ovum was much more bulky than it is now; but, whatever 



