BIGELOW: EARLY DEVELOPMENT OF LEPAS. 63 



Prof. E. L. Mark, who has carefully examined and criticised all my re- 

 sults and given me many helpful suggestions during the arrangement of 

 the results for publication. 



Durin'Tf several summers the work has been carried on in the Marine 

 Biological Laboratory and in the United States Fish Commission Station 

 at Wood's Hole, jNIass. I wish to express my appreciation of the assist- 

 ance, in the line of facilities for work, which was extended to me by the 

 officials of these two laboratories, particularly by their respective direc- 

 tors, Prof. C. 0. Whitman and Prof. H. C. Bumpus. 



II. Historical. 



The history of the development of our knowledge of the Cirripedia 

 has been so often written that for the purpose of this paper it is suili- 

 cient to give a mere outline. The now classical monograph of Darwin 

 ('51, '54) reviewed so exhaustively the knowledge obtained by earlier 

 observers, and added such a mass of original information on structure, 

 metamorphosis, relationships, and natural history, that in these respects 

 the Cirripedia have since ranked among well known groups of inverte- 

 brate animals. Since Darwin's time much of the investigation on the 

 animals of the group has been concerned with embryological develop- 

 ment, to which very little of Darwin's work was devoted. In the 

 " Challenger " Reports Hoek ('83, '84) made important additions to our 

 knowledge of the anatomy and relationships of many cirripedes, and gave 

 a good historical sketch of the group. Gerstacker's historical review in 

 Eronn's Klassen u. Ordnungen is exhaustive. 



The papers of Van Beneden ('70), Willemoes-Suhm ('76), Hoek ('76), 

 Lang ('78), Nassonow ('85, '87), Nussbaum ('90), and Groom ('94) deal 

 in more or less detail with embryonic development, and these papers 

 include the most important existing conti'ibutions to our knowledge of 

 cirripede embx-yology. Muller ('64), Filippi ('65), Mllnter und Buchholz 

 ('69) and Bovallius ('75) have made contributions regarding certain 

 points in the early development. 



Our knowledge of the early development of species of Balanus is due 

 principally to the studies of Miinter und Buchholz ('69), Hoek ('76), 

 Lang ('78), Nassonow ('85, '87), and Groom ('94). 



The early development of species of Lepas is known through the in- 

 vestigations of Willemoes-Suhm ('76), Groom ('94), and Bigelow ('96). 



The only recorded observations on the early development of Lepas 

 fascicularis earlier than those of the present writer are the published 



