418 W. E. RITTER AND M. E. JOHNSON 
line of least resistance, turns down into the cavity, and by the 
rapid growth of the zooids, soon breaks through the thin wall to 
the outside, the tip bending downward. 
d. The twist in the chain. The general character of this part of 
the chain may be seen from figs. 11 and 18, while the peduncles 
and blood vessels of the region are shown in the diagrams figs. 17 
and 18: Before the twist, we have within the parent, a straight 
double row of zooids with oral ends down. After it, the chain is 
turned back under the parent, and the zooids are again found with 
oralends down. Until the zooids break through the test to the out- 
side the chain has not begun to twist, the zooids still lying symme- 
trically along both sides of the median line. In fig. 13 thirty-six 
zooids are outside and the twist is just complete. The presence 
of two rows of zooids in the chain makes the turn appear more 
complicated thanit reallyis. The chainsimply doubles back under 
and then turns over, this turn being almost invariably to the left. 
This leaves the zooids with aboral ends again uppermost, but the 
row that was before on the left is now on the right side of the 
parent. 
e. Reduction of foot-pieces, first break in the chain,and formation 
of the first wheel. The first visible mtimation of the break-up of 
the chain comes in the peduncles and foot-pieces. The foot- 
pieces (fig. 17) gradually grow longer toward the distal end of the 
chain, coming to their maximum length a little before the end of 
the unbroken part is reached. After the maximum they shrink 
(fig. 22). The decrease is much more rapid than the increase, 
there being only about sixteen to twenty-four zooids in the di- 
minishing series. Fig. 19 shows that the first group consists of 
nine zooids whose peduncles have broken loose from the rest. 
The foot-pieces have shrunk still more and the distal ends of 
the peduncles have been drawn closer together. But while the 
foot-pieces, by which the zooids are held in the axial line of the 
stolon, become successively and rapidly smaller just before the 
beginning of the break in the chain, the zooids themselves are be- 
coming constantly larger. A consequent crowding of the zooids 
results. This brings about a pushing of the bodies of the zooids 
forward in the chain beyond the foot-pieces. The strain to which 
