CRUSTACEA. 79 



teristics of the higher Crustacea, that they did not undergo 

 a metamorphosis. It will not be uninstructive to advert 

 briefly to the observations, which have led to more correct 

 ideas on this subject. 



In a Dutch work, pubh'shed in 

 1778, there appeared the figure 

 of a small crustaccotis animal 

 (Fig. 53), unlike any previously 

 known. A French naturalist 

 took another in the Atlantic, 

 five or six hundred leagues 

 from the coast of France, and 

 included both under the generic 

 appellation of Zoea. A third 

 was taken in the course of Cap- 

 tain Tuckey's voyage to the 

 Congo, and two were observed Fig. 53. ZOEA (MAGNIFIED). 

 by Mr. J. V. Thompson when 



returning, in 1816, from the Mauritius. All the five speci- 

 mens were those of distinct species, and constituted the only 

 examples known of these Crustacea until the spring of 1 822. 

 In that year, Mr. J. V. Thompson, to his great surprise, met 

 with Zoeas in considerable abundance in the Cove of Cork. 

 Further research showed that these animals, which had been 

 regarded as so rare that the capture of each was recorded as 

 an event, were to be found in vast profusion in our bays and 

 estuaries ; and instead of being perfect and anomalous crea- 

 tures, were but the immature state of the common crabs 1 



The observations of Mr. Thompson, amply corroborated by 

 those of other naturalists, have established the fact, that the 

 Crustacea undergo metamorphoses; but to what extent this 

 takes place in the several tribes, we are as yet unable to de- 

 termine. Here is an ample field for inquiry, in which the 

 careful accumulation of facts, and even the collecting of 

 specimens, may render good service to the cause of science. 



The young state of the crabs, that to which the term 

 Zoea was formerly applied, exhibits, so far as known, a dif- 

 ferent appearance in each species. The one in which our 

 readers will be most interested is the common edible crab 

 (Cancer pagurus), and those who have only seen the 

 animal in its mature condition will perhaps be surprised 

 to learn that it existed at one time under the form reprc- 

 PART i. E 



