232 



EVENmeS AT THE MICROSCOPE. 



ordained that the little "Water-flea should be trans- 

 formed into a stony Acorn Barnacle. 



Having selected a suitable place for fixing its resi- 

 dence — such as those massive rocks which sustain the 

 impetuous billows on our sea-worn coasts — the great 

 projecting antennas manifest a new and unprecedented 

 function. Glands situated at their base secretfe a tena- 

 cioxis glue, which, being poured out in great profu- 

 sion, cements the whole front of the head to the rock, 

 including and concealing the antennte themselves. The 

 cement rapidly sets under water, and the animal is 

 henceforth immovable. 



It now moults its skin once more. Another great 

 change takes place ; the bivalve shell is thro^vn off, as 

 are also the eyes with their bent supports, and it is 

 seen to be a true Barnacle, though as yet of minute 

 dimensions, and with its valves in a very rudimentary 

 condition. It is now the representative of a third type 

 among the Crustacean forms, for it is in effect a Stoma- 

 pod ; such as the Opossum Shrimp {Mysis), for ex- 

 ample, with the shield composed of several pieces, 

 stony in texture, on account of the great development 

 of their calcareous element, and so modified in form as 

 to make a low cone the legs (become the oirri, or what 

 I have above called the " fingers") made to perform 

 their movements backwards instead of forwards, and 

 the whole abdomen reduced to an almost invisible 

 point. 



Marvellous indeed are these facts. If such changes 

 as these, or anything approaching to them, took place 

 in the history of some familiar domestic animal — ^if 

 the horse, for instance, was invariably born under the 

 form of a fish, passed through several modifications of 



