THE COLLAR-CELLS OF HETEROCGLA. 9 
The Collar-cells of Heteroccela. 
By 
George Bidder. 
With Plate 2. 
SUMMARY. 
Tue collar-cells are in normal life short and barrel-shaped, 
with separated cylindrical collars, which are never united. In 
certain pathological conditions, probably connected with suffo- 
cation, they elongate very greatly, diminishing in the diameter 
of their upper part, or “collum ;” and in some species, though 
not in Sycon compressum, the collars may then come into 
contact. In certain other pathological conditions the collar is 
lost, though apparently it can be regenerated. These meta- 
morphoses appear unconnected with the ingestion of food, which 
also was not found to induce any migration of the collar-cells. 
On the other hand, migration seemed to occur under excep- 
tionally unhealthy conditions. 
The collar is made up of (in Sycon compressum) about 
thirty parallel rods united by a film of some other substance. 
The flagellum is intimately connected with the nuclear mem- 
brane. There is an interstitial substance between the bodies 
of the cells. The area inside the collar appears to be provided 
with a sphincter membrane. 
Cells preserved and cut by the paraffin method show an 
average contraction of 5 : 4 linear in the best sections. In most 
preparations this contraction is uneven, producing Sollas’s 
membrane and other fictitious appearances. 
