278 PROCEEDINGS OP THE AMERICAN ACADEMY 



XXI. 



CONTRIBUTIONS FROM THE ZOOLOGICAL LABORATORY OF 



THE MUSEUM OF COMPARA'IIVE ZOOLOGY AT 



HARVARD COLLEGE. 



XXIIL— PRELIMINARY NOTICE ON BUDDING IN 

 BRYOZOA. 



By C. B. Davenpokt. 



Presented February 11, 1891, by E. L. Mark. 



Since several months must elapse before the publication of my studies 

 on Budding in Bryozoa, it has been thought best to present, in a pre- 

 liminary communication, some of the more important facts gained. 



In my paper on Cristatella,^ I described for that genus a mass of 

 cells lying between the ectoderm and muscularis which gave rise, by 

 active cell proliferation at certain regions, to the inner layer of the 

 polypide, — the layer from which the inner lining of the kamptoderm, 

 the outer layer of the tentacles, the nei'vous system, and the digestive 

 epithelium arise. This inner layer has been brought into prominence 

 by the conceptions of Hatschek concerning its significance, — concep- 

 tions which appear to have influenced some of his followers in their 

 study of marine Bryozoa. According to Hatschek, this inner- layer is 

 to be regarded as entodermic in origin, and to give rise to the digestive 

 epithelium only. The latter part of this view is certainly incorrect, 

 as shown by the concurrent testimony of Braem and myself It re- 

 mained, however, to determine the origin of the layer, or rather of the 

 stolonic mass from which it arises. The " stolonic mass " arises in the 

 embryo, soon after the completion of the two-layered condition, from 

 the ectoderm, at the same pole as that at which the so-called gastrula- 

 tion takes place. A disk of cells sinks below the general level of the 

 ectoderm and becomes overgrown by that layer. This disk expands 

 rapidly at the base of the ectoderm, and in all directions of the plane, by 

 cell proliferation, and gives rise to the first polypides. The first two 



* Cristatella: the Origin and Development of the Individual in the Colony. 

 Bull of the Museum of Comp. Zoul. at Harvard College, Vol. XX. No. 4, 

 November, 1890. 



