MUSEUM OF COMPARATIVE ZOOLOGY. 17 



Oue may therefore say that usiially the branches are median and oral, 

 the stolons lateral. Again, the branches give rise, like the primary stalk, 

 to two kinds of buds, branches and stolons. The stolons give rise only 

 to stalks of one segment each, bearing a calyx distally. These calyces 

 are so placed that their oral surface is directed towards the distal end of 

 the stolon. I have not found more than two individuals borne upon a 

 stolon. 



I have previously ('91, p. 72) tried to show how all buds in the stocks 

 of Bryozoa are to be referred back to embryonic tissue lying at the tips 

 or margin. In Endoprocta, however, the extreme tips seem to be oc- 

 cupied by a polypide, and the embryonic tissue lies in a zone at the base 

 of the latter. This difference may be regarded, however, as only appar- 

 ent, and the two conditions harmonized by conceiving the polypide in 

 Endoprocta retracted into the stalk, below the zone of embryonic tissue, 

 — the condition realized in Ectoprocta. The distal part of the stalk 

 will then become terminal, constituting an apical ring of embryonic tissue 

 surrounding the secondary atrial opening thus produced. From the oral 

 portion of this ring new buds — branches and stolons — are, as in Pluma- 

 tella, proliferated; and this process is repeated for each segment. At 

 (or near) the apices of these incipient branches and stolons lies a mass 

 of embryonic tissue which gives rise iu the one case — branches — to the 

 stalk, the polypide, and the Anlage of new buds; and in the other — in- 

 cipient stolons — to the stolon and the Aiilage of the individuals which 

 bud forth from it. The differences between the branch and the stolon 

 are, however, more apparent than real, as a comparison of the diagrams 

 Figures 59 and 60 (Plate VI.) will make clear. In one case (Fig. 59) 

 the mass of embryonic cells in any segment does not grow out far beyond 

 the youngest individual produced from it; in the other case (Fig. 60) 

 there is a considerable growth beyond the youngest individual. Thus in 

 the latter case a long stolon is produced, in the former it remains at a 

 minimum. 



As I have already stated, in most cases, particularly in young vigorous 

 stocks, one meets with the condition which may fairly be called typical, 

 in which from one segment three buds — one median (branch) and two 

 lateral (stolons) — arise. This typical condition may be expressed by 

 the formula on the next page. 



This formula will be understood by reference to the diagrams on Plate 

 VI., of which it is a symbolic expression. The lettei's represent in all 

 cases calyx-bearing individuals, the asterisks gemmiparous tissue. The 

 capital A stands for the individual which forms the main stem under 



