MUSEUM OF COMPARATIVE ZOÖLOGY. 47 
generation XXIV., reaches 3 maxima of XXVI., XXVII., and XXVIII. 
respectively, and falls again at the other margin to generation XXIII. 
In the subfan from which Figure 66 was taken, the curve begins at the 
outer margin with generation XVII., rises to generation XXII. at two 
points, and falls again to XX. at the inner margin of the subfan. 
Of the four proximal individuals in any fan here, as in Bugula turrita, 
the outermost, ancestral give rise to the greater number of individuals. 
In one case, for instance, the marginal individuals lie at the base of 31 
rows with 184 individuals, while the inner ones support only 7 branches 
with 65 individuals. Similar results were obtained from other stocks. 
With the middle of the primary individual as a centre, I passed an 
are of a circle through the extremities of the branches of a large camera 
drawing of a fan of B. flabellata, divided the radius into eighths, and 
passed arcs through these points. The number of individuals cut by the 
different arcs was then counted and tabulated; the arc with the longest 
radius cut through 87 individuals. By measuring the length of the ares, 
the number which should be cut by each arc on the assumption that the 
number of individuals per unit of arc is constant for all radii was deter- 
mined. This was then compared with the actual number found, with 
the following results: — 
ST | Me ete | TAM) Re a ne 4 N 
1 3 2} 5 87 40 
2 7 6 6 56 56 
3 13 13 7 68 70 
4 22 25 8 87 [87] 
In this instance, then, the 7th rule deduced for B. turrita evidently 
holds true for B. flabellata. 
While at Mr. Agassiz’s laboratory at Newport, during the summer of 
1890, I had frequent opportunity to examine other stocks of Bryozoa, 
which occur there very abundantly. I will take four species as typical 
examples of the groups they represent, and treat of the architecture of 
their colonies. 
Lepralia Pallasiana, Busk.'—It is not at all easy to determine 
1 I do not feel perfectly certain that the specimen shown in Figure 71 (Plate 
VIIL.) belongs to this species, because the characters of the young stocks differ some- 
