528 THE WONDER OF LIFE 



closed cradle ? It appears that at the time of hatching 

 there is a secretion from the embryo which acts as a solvent 

 on a weak seam at one end of the mermaid's purse. The 

 end gapes, and the miniature skate or dogfish works its 

 way out. Now it is interesting to find a parallel adaptation 

 in the far-separated bony fishes, where there is no egg- 

 shell, but only a firm shell-membrane. Both in the trout 

 (Trutta fario) and in the goldfish {Carassius auratus) 

 Wintrebert has found that the unicellular glands of the 

 embryo's skin secrete before hatching a ' peri- embryonic 

 fluid ' which has a digestive action on the shell-membrane. 

 It becomes more dehcate and finally almost hke wet paper, 

 being readily broken without any voluntary movement 

 on the part of the embryo-fish. 



A Difficult Case. — It must be admitted that some 

 adaptations are so remarkable that it is very difficult to 

 resist the intellectual temptation of supposing that they 

 arose in direct relation to the peculiar conditions. Let us 

 state the case in the words of a naturaUst who believes 

 that we are warranted in making the supposition which 

 seems to us at present illegitimate. 



' There is a fish ', Mr. J. T. Cunningham writes, ' which 

 has its eyes in a very remarkable condition. Spectacles 

 for human eyes are sometimes made, in which the upper 

 half has a curvature different from that of the lower. The 

 fish to which I refer, the Anabkps, which Hves in the 

 estuaries of Brazil and Guiana, does not wear spectacles, 

 but actually has its eyes made in two parts, the upper 

 half of the lens having a different curvature from that of 

 the lower. The pupil is also divided into two by prolonga- 

 tions from the iris. This fish is in the habit of swimming 

 at the surface with its eyes half out of water ; the upper 



