BIGELOW: EARLY DEVELOPMENT OF LEPAS. 121 



stages agree essentially with his account. His figures showing the 

 extension of the mesoblast closely correspond with those which 1 have 

 given and described, not with an idea of contributing new facts, but in 

 order to connect these stages with my account of the early development. 

 Groom interpreted the anterior growth of the mesoblast as taking 

 place on the dorsal side, and I shall later give confirmation of this 

 opinion, which rests on an orientation that I have used thus far without 

 adequate proof. 



IX. Formation of the Appendages of the Nauplius, and De- 

 velopment of the Organs- 



With regard to these phases of the development, my observations are 

 quite in harmony with the account by Groom ('94, pp. 151-154). A 

 few figures have been placed in this paper in order to show relations to 

 the early stages, but since there is such close agreement with Groom, it 

 is unnecessary to give a detailed description and numerous figures. 



Groom's important observation, that the appendages first appear on 

 the side which has the band of mesoblast, and that this is dorsal, is 

 supported by my Figures 91-94 (Plate 10) and 122-126 (Plate 12). ■ 

 All earlier writers on cirripede development had considei'ed the mesoblast 

 band as ventral (see i-eview of literature in Groom's paper). 



Figures 91 and 122 represent the first indication of the segmentation 

 of the embryo. Two transverse fui-rows {1, 2) appear on the dorsal side, 

 and extend around towards, but do not reach, the ventral surface. The 

 limit of extension of the transverse furrows corresponds closely with that 

 of the underlying mesoblast. The body is divided by the two furrows 

 into three regions, corresponding to the three segments of the Nauplius. 



Soon after the appearance of the transverse furrows there appears a 

 median longitudinal furrow on the same side (dorsal) of the embryo. 

 This is shown in transvei'se section in Figure 92 and in dorsal view in 

 Figure 125. This furrow intersects the two transverse furrows, but 

 does not extend to the extreme end of the embryo. Two new transverse 

 furrows now appear (3, 4, Figs. 93, 123-125), superficially dividing the 

 antei'ior and posterior segments of the Nauplius. Earlier writers have 

 published many drawings of these stages, and it seems unnecessary to 

 insert similar ones in this paper. 



The transverse furrows and the median longitudinal one deepen 

 rapidly, and cut off the three pairs of appendages, as has been correctly 

 described by Groom and earlier workers. The extension of the floor of 



