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Y. On the Development of Lepas fascicularis and the “ Archizoea” of Cirripedia . 
By R. yon Willemoes-Suhm, Ph.D., Privat-Docent in Zoology in the University of 
Munich , 'Naturalist to the 1 Challenged Expedition. Communicated by Professor 
C. Wyyille Thomson, F.P.S. 
Received September 28, — Read December 9, 1875. 
Burmeister’s important discovery that in Lepas the larvae pass through a Nauplius and 
a Cypris stage was made on the same Lepas which forms the subject of this paper. 
Burmeister*, however, had evidently only a ball of this Lepas, some specimens of 
which were young in the Cypris stage, which had just settled; while others were 
dismissing young Nauplii, which, unless great care is taken, die very soon in captivity. 
He thus missed the intermediate stages, which, however, were at that time much less 
important, as the first thing that was wanted then was to establish the general outlines of 
the Cirriped development. The Nauplius of this Lepas has since been seen by Darwin f, 
to whom Hancock showed it, “ calling his attention to a proboscidiform projection on 
the underside of the larva of Lepas fascicularis when just escaped from the egg.” 
Neither J. v. Thompson’s nor Pagenstecher’s observations refer, as far as I can find 
out here, to Lepas fascicularis ; and it seems not to have been taken up again as an 
object for embryological researches until Claus published his paper on the Cypris-like 
larva (pupa) of the Cirripeds and its metamorphosis into the fixed animal (Marburg, 
1869), a paper of which I have unfortunately only an abstract, as given by Nitsche in 
his embryological report for the year 1872, and by Claus himself in his ‘ Grundzuge 
der Zoologie,’ which, however, affords nearly all the information necessary for my 
purpose. My object is to give an idea of the whole development of one Lepas as 
accurately as possible, which seems never yet to have been done, as our whole know- 
ledge of the development of this group consists of fragments, collected mostly in the 
same way in which Burmeister gained his information. 
The materials for this paper were obtained during our cruise from Japan to Sandwich 
(June to July 1875), as we went along the thirty-fifth degree of latitude, when first very 
curious Nauplii, some of them 12 millims. long, were caught, which I identified at once 
with the nauplial form to which Dohrn has given the generic name of Arcliizoea%. In 
* £ Beitrage zur Naturgeschichte der Rankenfusser,’ 1843. 
f ‘ A Monograph of the Subclass Cirripedia : The Lepadidse.’ London, 1851, p. 11. 
+ Dohen, “ TTntersuchungen liber Bau und Entwicklung der Arthropoden. IX. Eine neue Ahup LAs -form 
(Archizoea gig as ) in Y. Siebold und Eoelieee’s Zeitschrift fiir wissenschaftliche Zoologie, Band xx. p. 597, 
1870. 
MDCCCLXXYI. 
T 
