84 
skeleton of Mitella. I am therefore greatly indebted to my friend 
Dr. Th. Mortensen, curator of the Zoological Museum at Copen- 
hagen, who gathered a most valuable material of Mitella (Polli- 
cipes) polymerus (Sowerby) Pilsbry at La Jolla, California, in 1915, 
and kindly placed it at my disposal for study. In a forthcoming 
paper dealing with his rich collections of Cirripeds from different 
parts of the Pacific Ocean I shall give the details of my studies. 
Here I intend to give only some few preliminary remarks serving 
to point out some principal lines of general interest concerning 
the phylogeny of the barnacles, and the theories cited above. 
As was the case in Scalpellum, the first plates which appear 
are also in Mitella the five „primordial valves“. They are devel- 
oped in the pupa-stage as five chitinous plates of porous structure 
soon after the pupa has fixed itself, and surround that part of the 
body which constitutes the capitulum of the young Cirriped. Very 
soon the calcification of the plates commences, and almost at the 
same time the Rostrum is seen, immediately followed by the de- 
veloping Latus superius. Then the upper row of Latera makes its 
appearance, and not till now do the first small scales of the stalk 
develop. 
The growth of the animal, especially that of the stalk, is al¬ 
most entirely restricted to the transition from capitulum to stalk, 
and only in this narrow zone of growth new plates or scales arise. 
Through the growth of the animal therefore, the scales of the stalk 
are soon removed from the transition-zone, and then almost com- 
pletely stop growing. The main growth of the plates of the capi¬ 
tulum takes place along the part of the plates facing the stalk. 
In its general features the development of the calcareous skel¬ 
eton in Mitella thus corresponds with Scalpellum. This, indeed, 
must be taken as contradictory to the theory that Mitella should 
be the ancestral type, and lends support to Darwins opinion, 
that the ancestors of both genera have had a skeleton consisting 
only of five capitulum-plates. Nevertheless we must take some 
reservation. We must look after the ancestors neither among recent 
genera nor among genera at present known from palæontological 
finds. In all probability the ancestral form of the stalked Cirri¬ 
peds (and thus of all the Thoracica) was a Cirriped with only five 
thickened parts of the mantie, or valves, viz. Carina, Terga, and 
