METAMOEPHOSES OF CRUSTACEA AND CIRRHIPEDS. 575 



as well as of the two large egg-capsules e, which, are attached to 

 it. Yet in its larval condition (fig. 313) it is an active little 

 creature, resembling in all essential particulars 

 the larvas of Entomostraca generally ; and from 

 this type the males do not depart nearly so much 

 as the females, the former retaining the general 

 plan of structure, as well as the activity of habits, 

 that prevail among the Entomostraca, whilst the 

 latter lose their instruments of movement, acquir- 

 ing the apparatus of suction and prehension. 



749. A still more remarkable example of meta- 

 morphosis is presented by the tribe of Cirrhipeds 

 ( 102), which, notwithstanding that they were 

 long ranked as Mollusks, on account of their shelly invest- 

 ment and their immovable attachment to solid bodies, are 

 now known to be so closely related to Crustacea, as in 

 the opinion of many naturalists to rank merely as a sub- 

 division of that group. The young, alike of the Lepas or 

 " barnacle," and of the Balanus or " acorn-shell," very much re- 

 semble those of the ordinary Entomostraca ; they possess eyes 

 and several pairs of motor appendages in this state ; and they 

 swim freely through the water, after the manner of water-fleas. 

 Before their last change, they are enclosed in a bivalve cara- 

 pace like that of Cypris ; and they then possess a pair of 

 large four-jointed antenna, which are well furnished with 

 muscles ; and it is by these antenna that the animal finally 

 attaches itself, by means of a peculiar cement which is poured 

 out from ducts running up into them from the body. In the 

 anterior of the recently-attached larva, the young Cirrhiped 

 may' be detected with its valves and cirrhi, like the embryo 

 insect in its pupa-case ; and the carapace and integuments of 

 the larva being thrown-off like a pupa-case, the perfect form 

 is disclosed. In most of these animals, as in many mollusks, 

 the sexes are united in the same individuals ; but when they 

 are separate, the males are minute imperfectly-formed crea- 

 tures, which lead a sort of parasitic life upon the surface of the 

 females ; and in some of the hermaphrodite species " supple- 

 mental males" are also provided. 



750. Among the Rotifera or Wheel- Animalcules, the double 

 mode of reproduction by agamic and by sexual eggs seems to 

 be the ordinary rule. The former may go on at a prodigious 



