
468 THE AMERICAN NATURALIST. | [Vor. XXXVI. 
close proximity. As a whole, the growth of the colonial polyps 
was much less forward than that of the isolated specimens. 
All were normal as regards the occurrence of the six pairs of 
primary mesenteries—four complete and two incomplete; the 
tentacles also were represented by a primary cycle of six exo- 
ceelic representatives and a secondary inner cycle of six 
entoceelic members. Variations and irregularities, however, 
were introduced in connection with the formation of the skele- 
ton. The epitheca was invariably produced at the free basal 
edge of the column wall, and under such conditions as those 
represented in Fig. 2, it is clear that its outline would be irreg- 
ular, and that the epitheca of one polyp would be in contact 
with that of the contiguous polyps to the extent the polypal 
walls were adherent. Likewise the basal disks of two polyps 
reclining against one another would be formed at a sharp angle. 
The septa of the colonial polyps exhibited from the begin- 
ning many irregularities and imperfections. Such a series is 
indicated in Fig. 3. The drawing was taken from the under 
surface of a living colony of seventeen polyps, adherent to 
a fragment of glass, and viewed by transmitted light, so that 
only the basal skeletal structures are exhibited. The polyps 
are seen to vary greatly in size; the outline is angulated where 
they are in contact with others, and rounded on the free 
border. The two larger polyps at each extremity of the colony 
partly overlap one another at an angle, though this is not very 
obvious from their flat basal expansions alone. The thickened 
margin to each polyp represents the epitheca, that of two con- 
tiguous polyps being fused along the line of contact. The 
basal disk is yet so thin as to be practically transparent and is 
indicated by the dotted areas. 
The radiating dark bands, as a rule simple, but sometimes 
forked, represent the adherent surface of the septa; the latter 
on account of their vertical thickness are non-transparent like 
the epitheca. In no polyp are the two orders of six septa fully 
or regularly developed in the manner already described for 
isolated polyps. Any number of septa from four to twelve are 
represented, as a rule with a suggestion of alternating large 
and small members. 
