40 BULLETIN OF THE 



cells iu the lateral bud aud the very early completion of its comtnu- 

 uication plate, the immediate needs of the polypide, which arises only 

 after the formation of the plate, being met by this supply of stored 

 uutrimeut.^ 



But why is the septum (communication plate) formed so early, if it 

 is desirable for the species that the growing tip should be well nourished 

 by the fluids of the body cavity 1 Here again I must resort to pure 

 hypothesis. I assume that the early formation of the septum is a pi'o- 

 visiou for the protection of the stock against a rapid influx of the sur- 

 rounding water iu case the brauch is broken. One can understand how, 

 if the body wall and growing regions depend upon the fluids of the body 

 cavity for nutrition, an open communication of this cavity with tlie out- 

 side world would be a serious obstacle to regeneration of the body wall in 

 the lost part, or the growth of the stock in any other direction. There is' 

 a fact which ought to be mentioned iu this connection, as bearing on this 

 hypothesis of the function of the septse. One frequently finds that in 

 stocks which have been handled with I'easonable cai'e the median branches 

 are broken off" at either end, and in almost everj' colony one or more lat- 

 eral branches are missing from the parent branch. Apparently, then, 

 the lateral branches are unusually subject to destruction, aud we find 

 the septse developed at a much earlier period between them and the an- 

 cestral branch than between individuals of the median brauch. Compare 

 Plate ir. Figure 14, in which the communication plate has not yet begun 

 to form, with Plate VI. Figure 58. 



III. Budding in Marine Gymnolsemata. 



1. Architecture of the Stock. 



I have already described the process of stock-building iu Paludicella, 

 and have attempted to show tliat it follows a certain law. I desire now 

 to present a few observations upon the architecture of certain stocks of 

 marine Gymnolsemata, which will aid in arriving at some general con- 

 clusions later on. Other observers have worked out the architectural 

 laws of single species or groups, and I shall refer to their studies either 



1 Similar conditions to those in Pahiclicella exist in some marine Bryozoa, and in 

 one of tliese cases, Bowerbankia, I find them fnlfiiled by a similar arrangement. Tiie 

 young buds of the stolon which give rise to the -'nutritive zooids" are, at an early 

 stage, loaded with food granules. As in Paludicella, so in Bowerbankia the 

 communication plates are formed early. 



