217 
His theory entirely foots on paleontology, and mainly on the faet 
that Mitella, according to the paleontologic finds, seems to be the 
oldest genus among our recent cirripeds, although only little older 
than Scalpellum. 1 ) Most later authors have followed Hoek, and 
Gru vel in his monograph (1905) adopts his theory, ranging among 
the ancestors also the extinet genera Turrilepas, and Loricula. The 
correctness of this mode of proceeding is not evident from his 
statements, and seems problematic also if we take into consider- 
ation their occurrence in time. In faet his reasoning seems to 
result in another theory, viz. that the more numerous the plates, 
the older the genus. — Neither Pilsbry nor Annandale in their 
memoirs have taken up a definite position as to the phylogeny; 
on the other hånd, Kriiger in his recent paper (1920) decidedly 
holds to Hoek’s theory. I shall return to his reasonings below. 
In a previous paper on Scalpellum (1912) I came to the con- 
clusion that Darwin’s opinions were in better accordance with 
the postembryonic development than Hoek’s theory, and in my 
preliminary note on the development of Mitella (1921) I again 
came to the same, although somewhat modified result. Studies of 
the details of the skeletal development of several species are put 
forth in this paper, and the results of these studies are of such 
importance from a phylogenetic point of view that I find it cor- 
rect to give a review of their bearing on classification before enter- 
ing on the detailed report on the species. 
A comparison with other crustaceans shows that the intensive 
secretion of lime in many cirripeds cannot be a primitive feature, 
and for this reason it may be doubtful, whether the heavily arm- 
oured forms are to be ranged among the „ancestral forms“ of the 
entire group. On the other hånd, such forms are more likely to 
be preserved as fossils than those without calcareous skeleton 
or with only a thin one. This faet at once weakens the import¬ 
ance of the evidences of paleontology in this case. Other facts 
likewise speak against the large number of plates as a prim¬ 
itive feature. In every case where we have succeeded in studying 
the development entirely, the pupa of the peduneulate cirripeds at 
*) Scalpellum even seems to occur earlier than Mitella (comp. Eastman, 
A. M.: Text-Book of Paleontology, Second Ed., Vol. I, London 1913, p. 
745); this would deprive Hoek’s theory of its last support. 
