64 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



notes of Willemoes-Suhm ('76), who died during the voyage of the 

 " Challenger " before his studies were completed. His paper gives a 

 very complete account of the history of the above mentioned cirripede 

 from the Nauplius to the sessile adult, but only a short and fragmentary 

 description of embryonic development. In some of the later embryonic 

 stages the observations are quite correct, but the few descriptions and 

 figures of cleavage stages are very inaccurate. 



The embryology of Pollicipes has been studied by Nussbaum ( ?9 ), 

 but his account is somewhat fragmentary. 



Among the Rhizocephalan Cirripedia the only description of a complete 

 series of embryonic stages is Van Beneden's ('70) account of Sacculina. 



Further, one or more of the investigators already mentioned has 

 studied the early development of species of the following genera of Cirri- 

 pedia : Conchoderma, Scalpellum, Tetraclita, Dichelaspis, Chthamalus. 

 However, much of this embryological work has been fragmentary, and 

 often superficial. 



The last, and by far the most important, paper on the early embry- 

 ology of the Cirripedia was published by Groom in 1894. This contains 

 a good resume of the previous work on the subject, reviewing the con- 

 tributions of the various investigators mentioned in the preceding para- 

 graphs. Groom studied the embryology of five species, namely, Balanus 

 perforatus, Lepas anatifera, I?, pectinata, Chthamalus stellatus, and Con- 

 choderma virgata. His observations on the later stages of embryonic 

 development and on the larval stages were exhaustive. The study of the 

 cleavage was undertaken secondarily, and was not investigated as accu- 

 rately as were the later stages. 



The accounts of the early embryology of cirripides which were given 

 by observers before Groom do not as a rule contain records of detailed 

 observation, which alone could be used comparatively in a paper from 

 the standpoint of cell-lineage. Groom reviewed well the general accounts 

 of previous investigators, and brought their results into line with his own 

 observations. In reviewing the literature I must necessarily deal pri- 

 marily with Groom's account, because he is the only investigator who 

 has attempted detailed description of the early stages of cirripede 

 development. 



III. Materials and Methods. 



The material upon which this paper is based was collected at Wood's 

 Hole, Mass., in the summers of 1894, 1895, 1898, and 1899. Prof. 

 Harold Heath of Stanford University, Cal., has collected and preserved 



