460 Prof. K. Grobben on the Genealogy and 



the Cirripedes and those of the Euphyllopods is to be inter- 

 preted as an adaptation which lias been evolved independently 

 in this lateral branch from foot-like mouth-organs. 



The Cirripedes therefore in all probability are of common 

 origin with the Copepods and sprang from Archiphyllopods, 

 as is also represented by Claus in his genealogical tree of the 

 Entoraostraca, and, moreover, they arose deep down from 

 forms which as yet showed no reduction of the mouth-parts. 

 This Archiphyllopod ancestral form of the Copepods and Cirri- 

 pedes belonged — and to this I would here attach especial 

 weight — according to its hahitus to the Apus-series. The 

 agreement to be detected in many respects between the Argu- 

 lidaj and Cirripedes indicates that the root of the former is to 

 be sought in the neighbourhood of the fork of the common 

 branch for Copepods and Cirripedes. 



The view that the Cirripedes and Copepods belong to a 

 common stem has not been undisputed. Thus it has been 

 represented by Balfour * that the Cirripedes are to be derived 

 directly from an old form of Phyllopod Avith two shells. The 

 development of the shell and also the possession of the paired 

 lateral eyes, as well as the larval history of the Cirripedes, 

 were the decisive points in Balfour's opinion. This author 

 regards the so-called Cj/^r/s-stage in the development of 

 Cirripedes as a phyletic one which " more or less accurately 

 represents an ancestral form of the Cirripedes," and he con- 

 siders that " both the bivalve shell as well as the compound 

 eyes are ancestral characters." To the similarity in shape at 

 this stage between the thoracic appendages and Copepod feet 

 Balfour attaches no great weight. 



Balfour is entirely correct in designating the compound 

 lateral eyes as ancestral characters ; but these constitute no 

 difficulty in the way of a common origin of Copepods and 

 Cirripedes, since the Argulidai possess the paired eye, and 

 rudiments of the lateral eyes are also formed in the Euco- 

 pepod Nauplius, but afterwards merely undergo degeneration. 

 On the other hand, it has already been shown that a close 

 comparison of the mantle-shaped Cirripede shell with the 

 bivalve shell-formations is untenable, and that it appears 

 possible to derive the shell of the Cirripedes from a shield- 

 shaped one. From this it appears that the peculiar formation 

 of the shell is a coenogenetic character of the larvae. And 

 yet it is simply and solely this superficial agreement of the 

 shell of the so-called Cyp7'is-stsigG with that of the Ostracods 



* F. M. Balfour, * Comparative Embryology,' German translation, 

 i. Bd., 1880, p. 482. 



