MUSEUM OF COMPARATIVE ZOOLOGY. 107 



of the colony-wall, which thus becomes the outer layer of the bud. 

 Hence the buds arise independently of each other. 



The second view is that advanced by Hatschek ('77, pp. 538, 539, 

 Fig. 3). He asserted that in Cristatella "Die Schichten der jiingeren 

 Knospe stammen vou denen der nachst alteren direct ab." Finally, 

 Braem ('88, p. 505) agrees essentially with Hatschek, and believes that 

 a typical double bud, although it does not always appear, is the funda- 

 mental condition. His preliminary account clearly shows that precisely 

 the same condition of affairs, except in so far as modified by the less 

 metamorphosed condition of the ectoderm, exists in Alcyonella as in 

 Cristatella. 



A. Observations. 



1. Origin of the Bud. — The result of my own work has been to lead 

 me to a conclusion differing from both of these two views, but more like 

 the second than the first. By my view, as well as by Braem's, Nitsche's 

 two types of single and "double" buds are united into one. I would not 

 say, with Hatschek, that the two layers of the younger bud arise directly 

 from those of the next older, but that each of the corresponding layers 

 of the younger and next older buds arises from the same mass of indiffer- 

 ent embryonic tissue. In some cases, each of the layers of the daughter 

 polypide does arise from the corresponding layers of the very young 

 mother bud. In other cases each of the two layers out of which the two 

 layers of the older bud were constructed contributes cells to form the 

 corresponding layers of the younger bud, but the cells thus contributed 

 have never formed any essential part of the older bud. All gradations 

 between these two types occur. For convenience* sake, we may always 

 call the older polypide the mother; the younger polypide, the daughter. 

 Figure 3 (Plate I.) shows a well advanced bud (Stage VIII.) which con- 

 sists of two layers of cells, an inner, i., composed of a high columnar 

 epithelium arranged about a narrow lumen ; and an outer, ex., of more 

 cubical cells. In a region (I) on the bud which is near the attachment 

 of its oral face to the body-wall there is a marked evagination of the 

 contour, caused in part by a thickening of the outer layer, and in part 

 by a slight increase in the diameter of the inner. This thickening o 

 the wall is the first indication of the formation of a younger bud, which 

 is to arise at this place. Figures 22, II., 16, VI. (Plate III.), and 11, 

 VI. (Plate II.) show later stages of buds originating in the same manner 

 as that of Figure 3. The mother bud has grown larger, as has also its 

 lumen. The outline in its upper oral region has become much folded as 



