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MANUAL OF ZOOLOGY. 



with the " cement-ducts " of the Cirripedes, and to be, there- 

 fore, really the homologues of the antennae. By their means, 

 the parasite draws nutriment from its host ; and as similar hol- 



Fig. 141. Morphology of Rhizocephala, A, First larval form of Sacculina purpurea, 

 greatly enlarged. B, Young of Peltogaster socialis attached to the abdomen of a 

 Hermit-crab ; at a the root-like processes of attachment of one individual are shown. 

 C, body of Sacculina carcini, of the natural size, the roots of attachment not 

 shown. (A and B are after Fritz M tiller.) 



low nutritive processes are developed on the " peduncle " of 

 certain Barnacles (Anelasma squalicola), there are grounds for 

 accepting Kossmann's view that the Rhizocephala are really to 

 be regarded as a degraded group of the Cirripedia. 



The embryos of the Rhizocephala (fig. 141, A) are at first 

 " naupliiform," with an ovate unsegmented body, an unpaired 

 median eye, and a dorsal shield or carapace. The abdomen 

 terminates in a movable caudal fork, and there is neither 

 mouth nor alimentary canal. In their second stage (as so- 

 called " pupae "), the young of the Rhizocephala are enclosed 

 in a bivalve shell, the foremost pair of limbs constitute pecu- 

 liar organs of adhesion ("prehensile antennae" of Darwin), the 

 two following pairs of limbs are cast off, and six pairs of 

 powerful biramose natatory feet are formed on the thorax. 

 There is still no mouth. The " pupae " now attach themselves 

 to the abdomen of Crabs, Porcellance, and Hermit-crabs ; they 

 remain astomatous ; " they lose all their limbs completely, and 

 appear as sausage-like, sack-shaped, or discoidal excrescences 

 of their host, filled with ova; from the point of attachment 

 closed tubes, ramified like roots, sink into the interior of the 

 host, twisting round its intestine, or becoming diffused amongst 

 the sack-like tubes of its liver. The only manifestations of 

 life which persist in these non plus ultras in the series of retro- 

 gressively metamorphosed Crustacea are powerful contractions 

 of the roots, and an alternate expansion and contraction of the 

 body, in consequence of which water flows into the brood- 



