MUSEUM OF COMPARATIVE ZOOLOGY. 17 
One may therefore say that usually 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 in the one case — branches — to the 
stalk, the polypide, and the An/age of new buds; and in the other — in- 
cipient stolons — to the stolon and the Anlage 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. Thusin 
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 letters represent in all 
cases calyx-bearing individuals, the asterisks gemmiparous tissue. The 
capital A stands for the individual which forms the main stem under 
