EPizoA. 275 



a second beneath it, which now incloses a body, altered in its shape 

 and in the number and nature of its appendages (Jig^ 120.). 



The process of moulting lasts from eight to ten 

 minutes. A great proportion of the original germ- 

 mass remains unaltered, surrounding the simple in- 

 testine, and extending into the bases of the tubular 

 feet of the larva. The nisus formativtis proceeds to 

 ^^^ flf^ g ja operate on this material, but on a modified plan. The 

 second body, which is formed inside the husk of the 

 first now cast ofij is divided into an anterior and a 

 posterior segment, the latter consisting of four joints. 

 A pair of four-articulate setigerous antennas diverge 

 from the anterior part of the body. Between the 

 Acbtheres : second antennae is the large single median eye, as in the mo- 

 **^^^' nocular Entomostracous Crustacea. The little Epi- 



zoon is now provided with five pairs of feet ; the first three pairs ter- 

 minate by a simple hook; the last two pairs are bifurcated, one 

 division being hooked and prehensile, the other tubular and emitting 

 tufts of bristles ; these natatory feet strike the water together, and 

 propel the body forward with a jerk ; they are aided by the last seg- 

 ment, which is terminated by four setigerous tubercles. 



The antennae probably serve to indicate to the young parasite its 

 appropriate object, to which it then proceeds to attach itself. The 

 first pair of feet is approximated towards the mouth, and forms the 

 uncinated mandibles. The second pair of feet increases in size, and 

 the terminal hook enlarges ; they serve to seize and hold on to the 

 surface of the fish selected. The feet of the third pair lengthen 

 and unite together to form a cartilaginous circular sucker, and per- 

 manently anchor the parasite to its prey. 



The two sexes are alike in their young and locomotive state: the 

 male at its final metamorphosis retains the first pair of feet as mandi- 

 bles, very similar in form to those of the female : the second pair is 

 shorter and thicker : the legs of the third pair always remain sepa- 

 rate from each other, and consist usually each of two large joints, 

 the last one terminated by a claw. The posterior natatory feet dis- 

 appear in both sexes ; and, with the loss of these instruments of loco- 

 motion, the eyes, also, are blinded and absorbed. 



Before proceeding to the Cirripedia, I would offer a few remarks 

 on the nature of the changes just described. They are commonly 

 spoken of under the same name as that given to the changes 

 of insects, and perhaps they differ only in degree. The metamor- 

 phosis in all insects is attended with the casting off of a certain 

 proportion of the precedent individual, called the "moult," or the 



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