Classification of the Crustacea. 461 



that occasions tlie similarity of this larval stage to the bivalve 

 Crustacean forms, while the shape of the thoracic feet, of the 

 abdomen, and of its furcal appendages completely exhibits 

 the Copepod character, and there is nothing in the way of 

 the interpretation of these features as being of phyletic value. 

 The absence of the second antenna is explicable as being due 

 to the mode of life of the Cirripedes, and to be understood 

 from the modification of the entire animal in consequence of 

 its having become fixed. In this connexion I would further 

 remark that the loss of the second antenna in the Cirripede 

 group has developed independently and is in no way to be 

 brought into genetic relation with the loss of the same appen- 

 dage in the existing Apodidae. 



The theories of Balfour are shared also by Fowler *, who, 

 however, in opposition to Balfour imagines a common origin 

 for the Cirripedes and Ostracods from Archiphyllopod forms, 

 and consequently goes even further than Balfour, who 

 supposes that the Ostracods originated independently from the 

 main Crustacean stem. 



In agreement with Balfour, Korschelt and Heider f also 

 assume that the Cirripedes arose from an Archiphyllopod 

 form provided with a bivalve shell and, indeed, resembling the 

 ancestral form of the Ostracods. In forming their decision as 

 to the ancestral form of the Cirripedes, Korschelt and Heider 

 likewise base their conclusions upon the Gypins-Wko, larva. 

 They assign no decisive value to the resemblance in the 

 formation of the thoracic appendages, nor to the agreement 

 between this larval stage and the Copepods with reference to 

 the number of the segments of the body, since these points 

 could have been acquired independently. On the other hand, 

 the presence of the large bivalve shell is considered to be of 

 primary importance, while after this the absence of the typical 

 Copepod characters (degeneration of the lateral eyes and of 

 the dorsal shield, and cleavage of the second maxilla into a 

 double pair of maxillipeds) in the so-called Gypris-l^^xYn of 

 the Cirripedes is also alluded to. 



With reference to the first-mentioned point I may appeal 

 to what has already been stated, and I would merely add that 

 I too, in forming a decision as to the common origin of the 

 Copepods and Cirripedes, attach no special weight to the 

 agreement in the number of the segments of the body in each 



* G. H. Fowler, " A Remarkable Crustacean Parasite, and its Bearing 

 on the Pliylogeny of the Entomostraca," Quart. Journ, Micr. Sci. vol. xxx. 

 1890, pp. 115-119. 



t Korschelt and Heider, "■ Lehrbuch der vergleichenden Entwicklungs- 

 geschichte der wirbellosen Thiere. — Specieller Theil," ii. Heft, pp. 500-501. 



