MUSEUM OF COMPAKATIVE ZOOLOGY. 71 



primary polypides, or rather the primary and secondary one. Moreover, 

 as the series of sections shows, the stolon does not exist merely in this 

 section, but it is a disk which is cut here in one of its diameters. A sepa- 

 ration of the stolonic mass has occurred between the two oldest polypides, 

 so that the ectoderm is here in contact with the coelomic epitlielium, 

 just as is the case between buds iu the adult stock. As the colony in- 

 creases, the inner and outer margins of the stolonic tissue continue to 

 extend farther outward, and this tissue forms at first a broad ring of 

 ever increasing diameter. Later, as the area of the stock increases, the 

 ring becomes broken, so that, instead of growing along an infinite number 

 of radii, its growth is confined to a few, as in the adult colony. 



I will defer a discussion of the significance of these facts to the gen- 

 eral part of this paper. 



B. GENERAL CONSIDERATIONS. 



I. Laws of Budding. 



Carefully conducted studies on stock building have generally revealed, 

 just as these on Bryozoa have shown, a law in budding. This law in 

 budding results in the formation of a stock the interrelation of whose 

 individuals is a determinate one. I now propose to ofi"er an hypothesis 

 to account for the existence of these laws, and then to show how facts 

 of budding in Bryozoa and other groups can be explained by means 

 of it. 



And first of all I must acknowledge that this hypothesis, although 

 perhaps here first formulated, really depends upon observations and de- 

 ductions made long ago on this group, first by Hatschek, who from 1877 

 has maintained that individuals do not arise independently of one an- 

 other, and secondly and mostly to Braem, who in '88 (pp. 505, 506) 

 declared of Phylactolsemata "dass in dem Stock keine Knospe entsteht, 

 die nicht auf das embryonale, d. h. den specifischen Leistungen der 

 Korperwand noch nicht angepasste Zellmaterial einer alteren Knospen- 

 anlage zunickgienge und dass somit iu der ersteu Knospe des keimen- 

 den Statoblasten sammtliche Knospen des kiinftigen Stockes implicite 

 enthalten sind." Xot less is the following hypothesis indebted to the 

 ideas of Roux and Fraisse, and to Nussbaum, who has said ('87, p. 

 293) : " Ein lebendes Wesen ist somit als Ganzes oder in seinen Theilen 

 soweit individualisirt und verganglich, als die Gewebebildnng und die 

 Theilung der Arbeit vorgeschritten ist ; das Ueberdauern der Einzelexis- 



