CmiUPEDlA. 



277 



of these various instruments. The outer case, and all that gave form 

 and character to the precedent individual, perish and are cast off; 

 they are not changed into the corresponding parts of the new indi- 

 vidual. These are due to a new and distinct developmental process ; 

 rendered possible through the retention of a certain proportion of the 

 unchanged germ-cells. The process is essentially the same as that 

 which developes the cercariform larva of the Distoma within the 

 gregariniform one, or the external bud from the Hydra, or the in- 

 ternal bud from the Aphis. It is a slightly modified parthenogenesis ; 

 and the phases by which the locomotive anellidous larva of the Lernsea 

 passes through the entomostracous stage before retrograding to the 

 final condition of the oviparous, limbless, bloated, and rooted parasite, 

 are much more those of a metagenesis than a metamorphosis. 



I now proceed to the second class of Articulated animals which are 

 associated in the present Lecture with the Epizoa. 



Many of the Cirripedia* are parasitic animals, like the Epizoa, but 

 are dependent upon the organised bodies to which they are attached 

 for their place of residence, not for their food ; those Cirripeds which 

 do not infest other animals are attached to sea-weed, floating timber, 

 121 or rocks. The Cirripeds are 



symmetrical animals, with a 

 soft, obscurely articulated body 

 enveloped in a membrane (Jig- 

 121, c c) ; they are provided 

 with six pairs of thoracic feet 

 (ib. A), divided into three 

 joints, and terminated each by 

 a pair of long and slender, 

 many-jointed, ciliated tentacles, curled towards the mouth, whence 

 the name of the class. They are androgynous, and in some species 

 there are also small males parasitic on the bisexual individuals. f 

 The mouth (ib. a) is prominent, and, in most species, provided 

 with a broad upper lip, with two palps or feelers (ib. h), and three 

 pairs of dentated and ciliated jaws. The opposite extremity of 

 the body is prolonged into a slender, many-jointed, ciliated caudal 

 appendage {fig- 123, g), which is traversed by the generative 

 canal. The mouth is situated near the anterior extremity of the 

 body, which is modified to form the organ of attachment of the 

 animal. It is sometimes produced to a considerable extent, and is of 

 contracted diameter, forming a long and flexible peduncle ; sometimes 



I a d 

 Lepaj anatifera. 



Lat. cirrus, a curl, pes, a foot. 



t CCXXIIL pp. 189. 248. 



t3 



