MUSEUM OF COMPAEATIVE ZOOLOGY. 3 



When the stock is studied more carefully, it is seen that the individ- 

 uals which compose it are arranged one in front of the other, forming 

 lines. (Figs. 1, 2, 2\) We may distinguish (1) a single primary branch, 

 which forms a continuous line from the oldest individual, which has been 

 derived directly from the egg, to the terminal one ; and (2) secondary 

 branches, which arise from the individuals of the primary branch and at 

 right angles to their axes. Typically, a secondary branch arises from botli^ 

 the right and left sides of each adult member of the primary branch, but 

 in some cases the secondary branch of only one side appears to be formed. 

 The secondary branches are composed, like the primary, of a continuous 

 line of individuals placed end to end. These in turn give rise to ter- 

 tiary branches, which run out at right angles to the right and to the 

 left of the secondary ones, and hence parallel to the primary branches. 

 Quaternary branches may occur in like manner, but I have never seen 

 branches of a higher order than the fourth. All of these branches may 

 lie in one plane, but frequently some of the lateral buds are so placed 

 that they give origin to secondary branches which rise above the plane of 

 the object upon which the stock lies. A study of Figure 1 and the cor- 

 responding diagram. Figure 2, reveals some additional facts. The two 

 lateral buds of an individual do not arise at the same time, and there is 

 a tendency for the first, and therefore oldest and most developed, sec- 

 ondary branches to arise alternately on opposite sides of the primary 

 branch. This last rule has many exceptions, however. 



The long axis of the individual coincides with that of its branch ; the 

 sagittal plane lies in that axis, and at right angles to the substratum. 

 The atrial opening is near the distal end of the individual in the sagit- 

 tal plane, and is turned away from the substratum. The anal aspect of 

 the polypide is placed nearer the tip of the branch, — hence distad ; 

 the mouth, on the contrary, proximad. 



A very casual observation shows that not all branches nor all individ- 

 uals are of the same size. The shortest and therefore youngest branches 

 are placed most distally, and are seen as small buds. The terminal indi- 

 viduals of the branches are also evidently less well developed than the 

 more proximal ones. The adult individuals measure from 1.5 to 2.0 mm. 

 in length and from 0.30 to 0.35 mm. in widbh. The younger individ- 

 uals differ from the older in form also. The outline of the adult branch, 

 looked at from the side, and disregarding the atrial opening, is formed by 

 a series of beautiful sigmoid curves (Fig. 9). The concave and convex 

 points of the upper and lower sides of an individual are not placed exactly 

 opposite each other, and the lower (abatrial) side approximates more 



