>8 JAMES FRANCIS ABBOTT, 
The central filamentous cord which is derived from the denser 
cytoplasm immediately surrounding the nucleus persists as the 
straight axial filament of the differentiated cell. 
It will be noted that each colloblast, developed as described 
above is formed from a single primitive formative cell, not from 
two cell-elements as described by Samassa. Each one is developed 
independently in ©. maitsukurü, while in C. willeyi they appear to 
arise in groups as described by Samassa for Beroe. A sheet of 
colloblasts in C. willeyi, developing together, is covered by a thin 
membrane derived from the cells themselves, each one of which is 
attached to it by means of its apical filament. 
The muscular core. The arrangement of the muscular 
strands of the tentacles is quite complicated and ditfers considerably 
in the two species of Coeloplana. In C. mitsukurü there are two 
sets of muscles making up the core of the secondary tentacles, — 
longitudinal and diagonal. The outermost layer is a thick sheath 
of longitudinal muscle fibers in which the colloblasts are rooted. 
The cavity surrounded by this sheath would appear as a tube, were 
it not for two partitions which run lengthwise of the tentacle and 
divide the inner cavity into three longitudinal chambers. The tissue 
of the outer wall and of the partitions appears to be continuous. 
Within the three chambers just mentioned, are located the short 
diagonal muscle fibers. In longitudinal section these have somewhat 
the feather like appearance to be seen in the body muscles of the 
earthworm. There is a difference however in that the short diagonal 
bundles in Coeloplana arising from the walls formed by the longi- 
tudinal muscle fibers focus, as it were, In a common point in the 
center of the cavity. The repetition of these focal points at regular 
intervals longitudinally of the tentacle, gives in section the appearance 
of apices of a series of wedges as described above. The series of 
diagonal muscle bundles arise however from the whole inner surface 
of the chambers. Filling the spaces between, there is a sort of loose 
connective tissue full of large irregular cells that resemble wandering 
giant cells. 
In ©. willeyi there are two sets of circular and two of longi- 
tudinal muscles. The spiral filaments of the colloblasts are inserted 
in an outer sheath of muscle fibers. Within this wall are five con- 
spicuous bundles of longitudinal fibres arranged in a quincunx (in 
cross section). About the central cord of the five is a dense sheath 
of circular muscles. There are no longitudinal chambers as in the 
