160 LECTURE XIII. 



of the animal and the lining membrane of the shell. The ova are doubt- 

 less irajiregnated in attaining this situation : here they increase in size, 

 and change their colour to pink and then to white : the embryos are 

 here developed, and, after their escape, all traces of the temporary 

 receptacles disappear. This view of the generative organs seems to be 

 the true one, provided the Cirripedes be androgynous. 



When we reflect on the uniformity of distribution of the Cirripedes, 

 particular species being attached to particular objects, and these not 

 always stationary and extended bodies, but often living animals, and 

 sometimes animals with quick powers of locomotion ; when we further 

 call to mind that they adhere, not by prehensile jaws or feet, but by 

 the growth of a jiedunculated root, or by the gradual application of a 

 layer of cement forming the base of their shell, we must be convinced, 

 that the organization and properties of the sedentary Cirripede are 

 wholly inadequate to afford an insight into the process by which it 

 acquired its resting place, and, that a knowledge of its previous career 

 from the time of quitting the egg is not less essential to an explanation 

 of the subsequent attachment of the Cirrijiedia, than it was for the elu- 

 cidation of corresponding phenomena in the Epizoa. 



No fortuitous dispersion of ova giving origin at once to a pedun- 

 culated or sessile multivalve can account for the invariable attachment 

 of the Coronula to the skin of the whale, and of the Otion to the shell 

 of the parasitic Coronula ; of the Chelonobia to the carapace of the 

 turtle, of the Cineras to the tail of the sea-serpent, or of the imbedding 

 of the Acasta in the substance of a sponge. These remarkable phe- 

 nomena have been explicable only since the discovery of the singular 

 metamorphoses which the Cirripedes undergo, and of the power which 

 they possess at one period of their existence of attaining and selecting 

 their peculiar and appropriate place of permanent abode. Nor were 

 the real nature and affinites of this singular shell-covered class of 

 animals less problematical and doubtful before the phenomena of 

 their development had been traced out. 



Mr. V. Thompson, whose mi- 

 nute and careful researches 

 into the natural history of ma- 

 rine animalcules have thrown 

 so much light on the structure 

 and development of radiated 

 Young of Baianus. animals, was also rewarded by 



the discovery of the metamorphosis of the Cirripedes. On the 28th 

 April, 1823, he captured, with a small muslin towing net, a number of 

 translucent animalcules {Jig. SI.), about the tenth of an inch in length. 



d 



