Classification of the Crustacea. 457 



ment of many organs which ensue from these conditions. In 

 the case of the Cirripcdes it is chiefly the developmental 

 stages that furnish the evidence necessary for the question of 

 origin. 



Among the Cirripedes the Lepadidaj (forms like Pollicipes*) 

 are to be regarded as the most primitive. The first thing 

 which strikes us in the organization of this family, besides 

 the peduncle-shaped develoj)inent of the cephalic end, is the 

 complete enclosure of the body by a mantle-shaped shell. 

 The mouth-parts are short, the mandibles devoid of palj)s, 

 the two pairs of maxillae small. Of the two antennai the 

 second has disappeared, while the first serves as an organ of 

 attachment. The six pairs of thoracic legs are provided with 

 long many-jointed rami thickly clothed with seta3, and the 

 abdomen appears to be completely reduced. 



Above all, the mantle-shaped shell reminds us of the bivalve 

 shell of the Eslherida;, and would afford justification for a 

 derivation from Archiphyllopods resembling Estheria. Yet 

 a closer consideration of the developmental stages shows that 

 such a derivation is incapable of accomplishuient, since these 

 stages structurally conform to the conditions found in the 

 Copepods and in the Apodidce among the Euphyllopods. 



The extensive structural agreement between the develop- 

 mental stages of the Cirripedes and those of the Copepods 

 was demonstrated by Pagenstecher t and Claus J. The 

 Cirripede Nauplius closely resembles the Copepod Nauplius, 

 and in the so-called Cypris stage the shape of the thoracic 

 feet as swimming-appendages, as well as the segmentation of 

 the abdomen and the formation of the furca, repeat the con- 

 ditions which exist in the case of the Copepods. 



Since the idea that the Cirripedes are closely allied to the 

 Copepods appears to be thoroughly in accordance with facts, 

 it must also be possible to derive the Cirripedes, like the 

 Copepods, from Archiphyllopods which possessed the habitus 

 of Ajms. As a matter of fact, such points of agreement with 



* Cf. A. Weithofer, " Bemerkungen iiber eiae fossile ScaIj>el/ian-Art 

 aus dem ScMier von Ottnang uud Kreuismiinster, sowie iiber Cirripedien 

 im Allgemeinen/' Jahrbuch der k. k. geolog. Reichsanstalt, 1887, 37 Bd., 

 p. 370. 



t A, Pagenstecher, " Untersuchungen iiber niedere Seethiere aus 

 Cette. — IX. Beitrag zur Anatomie und Entwicklungsgeschichte von 

 Lepas pectiuata,'' Zeitschr. f. wiss. Zool. Bd. 13, 18ft3. 



X C. Claus, "Die CVpris-ahnliche Larve (Puppe) der Cirripedien und 

 ihre Verwandlung in das festsitzende Tliier," Schriften der Gesellsch.^zur 

 Beforderung der gesamniten Naturwiss. zu Marburg, Supplementheft v., 

 1869. Also ' Untersuchungen zur Erforschung der genealog. Grurdlage 

 des Crustaceensystems,' pp. 79-88. 



