72 BULLETIN OF THE 



tenz, die Theilbarkeit auf geschlechtlichem oder ungesclilechtlichem 

 Wege, spontau oder kiiustlich bedingt, ist an das Vorhaudcnsciii undif- 

 ferenzirter Zellen gebuuden uud ist luu so grosser, je weiter iui Orgauis- 

 miis diese Zellen verbreitet sind"; and, finally, to the idea which is 

 implied iu the conclusions of Nussbauru ('80, pp. lOG-113) and Weis- 

 maun, that gerniplasma does not find its origin in the parent individuals, 

 but is merely borne by them in its unbroken passage from generation 

 to generation. 



This hypothesis is simply that there is in every stock of Bryozoa a mass 

 of indijferent ceil inaterial which is derived directly from indifferent cells 

 of the lai'va or embryo, and whose function is to form the organs of the va- 

 rious individtials, including the polypides. Tiiis indifferent cell material 

 lies in the body wall, principally at the growing tip or margin of the 

 stock. By its growth and differentiation it gives rise to the body wall, 

 muscles, etc., and at intervals it leaves behind, as a portion detached 

 from itself, a mass of indifferent cells, which is capable of forming a polyp- 

 ide, or of becoming a new centre of growth, or of both. Which of these 

 possibilities will be fulfilled, where and when these masses of indifferent 

 cells will be left behind, depends upon the necessities of the species, and 

 the variations in these respects give rise to the peculiar characters of 

 the different stocks. 



This hypothesis differs from that of Braem in that the pre-existence 

 of a Knospenanlage assumed by Braem is, according to my view, a non- 

 essential feature in the formation of the colony ; the pre-existence of an 

 indifferent cell mass, which does not itself constitute buds, but may give 

 rise to masses which can, is the only essential feature. 



As a first application of this hypothesis I refer the reader to the con- 

 ditions of stock formation in Paludicella, already described. We find at 

 the tip of the colony a mass of large proliferating cells, which I regard 

 as histologically undifferentiated. These cells give rise to the body wall, 

 — the cystid, — and at intervals leave behind three masses of cells, which 

 I regard, from the fact that they retain their cuboid condition, as well 

 as from their ultimate fate, as indifferent or embryonic. The median 

 mass of each of these gives rise to a polypide, and to one only. The 

 lateral masses form centres of growth similar to the one from which they 

 ■were derived. 



In order to reproduce the arrangement of individuals in the stock re- 

 sulting from this manner of budding, we may make use of some graphic 

 method of representation, as Smitt ('65% pp. 139, 140) did long ago, and 

 as Allman (70), Semper ('77, pp. 67-78), Chun ('88, pp. 1167-1180), 



