56 James Francis ABBoTT, 
muscle from which arise in one plane at regular intervals. the se- 
condary tentacles. These are independently contractile. The ulti- 
mate branch never arises directly at the tip of the main stalk but 
always at one side in conformity with the arrangement of the others. 
The secondary tentacles are covered with typical Ctenophoral ad- 
hesive cells (lassocells, colloblasts) that sometimes, when the ten- 
tacle is fully extended, appear to be arranged in groups or batteries, 
especially in the region near the end of the primary tentacle. As 
a rule, in C. mitsukurii, there are no such cells on the primary 
tentacle itself, except near its origin. In C. willeyi, however, the 
primary tentacle appears to be covered uniformly with adhesive cells. 
The masses of undifferentiated cells in the accessory tentacle and 
the muscles of the tentacle root are penetrated in all directions by 
the branches of the canals of the gastric system, as already described. 
Histological structure. 
The adhesive cells or colloblasts are of the type described and 
figured for typical Ctenophores (CHux, 1880; Hertwic, 1880; 
ScHNEIDER, 1892; Samassa, 1902; Bourne, 1900). In especially well 
fixed material certain details of structure may be brought out in 
Coeloplana which differ slightly from the appearances described by 
previous investigators. The fully developed cell consists of a sub- 
globular or bellshaped cap, surmounting a rather thick spiral filament 
which is inserted in the outer muscle layer of the secondary tentacle. 
The shape of the cap seems to vary with age. In younger cells it 
is almost globular. Frequently in cells remote from the original 
formative tissue, it is elongated. Whether this is a result of growth 
or of differentiation persisting from the beginning could not be deter- 
mined. In ©. mitsukurii the globular form seems to be the only 
one. The apex of the cap is usually drawn out to a fine filament 
and the lower margin is likewise expanded into a delicate frill or 
skirt. Within the outer membrane of the cap-cell, the granular 
cytoplasm is arranged in a hemispherical layer of segments set like 
paving stones. in the center of which the nucleus lies, just above. 
the insertion of the spiral filament. Within the spiral coil is a 
delicate thread running through the axis of the spiral and uniting 
with the latter just before its insertion in the tentacle. The spiral 
may be either dextral or sinistral, and the two kinds usually occur 
in equal proportion, side by side. Looked at from below, the cell 
appears as a cup into the depression of which is inserted the spiral 
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