
466 THE AMERICAN NATURALIST. [Vor. XXXVI. 
sharp contrast with this the unfixed larve remained all the 
time at practically the same stage as when first extruded. 
The glass vessel to which some of the polyps became adher- 
.ent was broken into small fragments, with the polyps still upon 
them. These could then be transferred from one aquarium 
to another, or examined in small dishes as transparent living 
objects under the microscope. In this way the growth of the 
various organs was followed day by day. Some specimens 
were kept alive for a period of seventeen weeks, the develop- 
ment of the tentacles and septa being followed as far as the 
third cycle. For the present purpose the normal development 
will be succinctly reviewed, so as to compare the modifications 
introduced as a result of the primary grouping of many of the 
polyps in colonies. 
On fixation the tissues of the polyps became transparent and 
the six pairs of primary mesenteries were seen to be already 
present, four pairs attached to the stomodaeum and two pairs 
incomplete. About, a month elapsed before the members of 
the second cycle began to appear, being first represented by a 
pair in each of the dorsal exocceles, then later by a pair in each 
of the middle exocceles, and finally by a pair in each ventral 
exoccelic chamber. 
The first tentacles commenced to make their appearance two 
or three days after settling, as six rounded outgrowths over 
alternate mesenterial chambers, and early showed an opaque, 
white, knob-like apex distinct from a short, more transparent 
stem. The six prominences appeared simultaneously, con- 
stituting a first cycle, and were equal in size and distance 
apart, and in communication with the exoccelic chambers. 
About four weeks passed before another cycle of six tentacles 
appeared, internal to the first, and situated over the entocoelic 
chambers. The further tentacular development was somewhat 
complicated and need not be here considered. 
Three or four days after fixation the skeleton was first 
bserved in the form of six radiating septal upgrowths, prac- 
tiodlly equal in size. At the same time a narrow peripheral 
calcareous ring was formed, its outer surface uncovered by the 
soft polypal tissues, and therefore to be regarded as an epitheca. 

