V 



108 BULLETIN OF THE 



rial before the formation of the communication phite, and yield it up to 

 the rapidly growing bud. 



Tlie regenerated polypides, like the marginal ones, arise in Cheilo- 

 stonies in a definite position, — on the wall of the operculnm from tissue 

 left behind to give rise to the polypide, but not- wholly used up in its 

 formation. They arise wholly from the body wall, come to lie next to 

 the " brown body," and cause its disintegration. 



The more important theoretical conclusions to which I have arrived 

 are : — 



a. There is in every stock or corm of Bryozoa a mass of indiflferent 

 cell material, which is derived directly from the indifferent cells of the 

 larva or embryo, and whose function is to form the organs of the different 

 individuals, including the polypides. This mass by constant growth and 

 division affords the embryonic material for lateral branches. 



b. The form of the stock and interrelation of individuals is in large 

 part controlled by food supply. 



c. The inner layer of the Phylactolaematous larva represents meso- 

 derm only : the entoderm has become rudimentary through loss of the 

 alimentary function. 



d. The polypides arise in Phylactolteraata at the pole of ingression, 

 •which is probably homologous with the aboral pole of Gymnolsemata. 



e. The inner layer of the polypide bud is composed of cells derived 

 from the rim of the blastopore, and they are to be regarded as still 

 indifferent, and as first becoming differentiated into ectoderm and ento- 

 derm in the formation of the young polypide. 



/. Gemmiparous tissue is a rapidly assimilating tissue possessing 

 large nuclei because actively assimilating, and staining deeply because 

 full of food material. 



g. Tlio Endoproct and Ectoproct larvse are to be compared by assum- 

 ing that the act of rotation of the axes occurring in the former has been 

 leaped over in the ontogeny, the mouth and anus arising at once on the 

 pole opposite the blastopore. 



Cambridge, Mass., June 1, 1891. 



