26 BULLETIN OF THE 



sional nuclei. These are the tubular cells already referred to. Some of 

 them contain the agglutinated cilia characteristic of flame cells, and they 

 arise from large cells, which must indicate the beginnings of the excretory 

 tubules of the stalk already mentioned. 



What is the meaning of the fact that no younger stages than these 

 occur, although such and all older stages are abundant] Have these 

 young stocks been derived from fertilized eggs, or have they some other 

 origin 1 



I have already referred to the fact that the great mass of the buds of 

 any Urnatella stock are found at the upper end of the parent stalk. The 

 lower and middle parts of the stalk possess few buds, although they once 

 constituted the upper end of the stalk. "What has become of the buds 

 which have been lost] Leidy asked this question, and the facts led him 

 "to suspect that the branches are spontaneously and habitually detached 

 from the parent stem, to become elsewhere attached, and thus form new 

 colonies." I have evidence that raises the suspicion of Leidy to as near 

 certainty as can be obtained by use of the morphological method. The 

 " youngest stocks " are derived from the stolons of the ■parent stalk, which 

 habitually become free for the purjyose of founding new stocks. 



To establish this proposition it will be necessary to show, (1) identity 

 of structure between old lateral buds and young stocks, and (2) the 

 scar of attachment of the young stock to the parent stalk (cf. Plate VI. 

 Fig. 58). Of identity of structure there can be no question. Often it 

 would have been quite impossible to distinguish between young stocks 

 and "stolons" which had been violently broken off from the parent 

 stalk and were lying loose in the bottle, were it not for a single criterion, 

 namely, the young stocks had dirt adhering to their lower surface. An 

 application of the second criterion leads to the same positive result. In 

 series of thin sections of young stocks one can always find at one side 

 of the median plane the scar of former attachment, which appears as a 

 thickening of the cuticula into which ectodermal cells may sometimes be 

 seen penetrating (Plate V. Fig. 47). We have here, then, a method of 

 non-sexual propagation quite similar to that obtaining in Loxosoma, where 

 the buds habitually drop off, so that this genus is commonly said not to 

 be stock-producing. This resemblance must be regarded as being purely 

 a physiological one, and not in the least implying any closer relation- 

 ship of the two genera. 



I have already expressed my belief that the stolons are thrown off reg- 

 ularly for the purpose of founding new stocks. On this assumption we 

 can account for the rapid growth of the embryonic tissue giving rise to a 



