244 '^- Playfäie Mc Murrich, 



sphincter muscle (Fig. 28), completely imbedded in the mesog-loea. 

 It is very weak and lias a delicately reticular structure, the tra- 

 beculae separating- the meshes beiiig- very delicate. The muscle cells 

 are few in number and exceeding'ly small, the majority of the meshes, 

 indeed, seeming at first sig'ht to be mere empty Spaces. The small- 

 ness of the muscle fibres is, however, a characteristic of the circular 

 musculature of the column and there can be no doubt that the 

 reticulum represents the sphincter and is not merely loosely arranged 

 mesog'loea. At the upper part of the scapus cavities occur in the 

 mesogloea, some scattered and others ag-gregated to form a reticulum 

 whose trabeculae are much thicker than those of the capitular 

 sphincter; these seem to constitute a second sphincter. 



The tentacles are very thin-walled except toward the tips, where 

 the extra thickness is probably due to a little extra contraction. 

 Their ectoderm is thicker than both the mesogloea and endoderm 

 together; the longitudinal muscles are but feebly developed and are 

 situated in the ectoderm. Brownish pigment granules occur in the 

 endoderm, especially toward the tips, and it is also present in the 

 endoderm of the column and disc. The structure of the disc is 

 essentially similar to that of the tentacles. 



The stomatodaeum is irregularly ridged longitudinally and 

 possesses two siphonoglyphs. The mesenteries of the flrst three 

 cycles have a well developed longitudinal musculature wliich occupies 

 nearly the entire surface of the muscular portion of the mesenteries 

 and consists of numerous slender and branching processes which 

 diminish in height somewhat gradually toward the outer edge of 

 the muscle, but abruptly at the inner edge (Fig. 26). The basal 

 portions of the mesenteries bear several short, rather stout, unbranched 

 processes, but there is no distinct fold representing a parieto- 

 basilar muscle, nor do tangential sections through the base reveal 

 a distinct basilar. Keproductive cells in very early stages of 

 development were seeu in some ofHhe mesenteries of the second 

 and third cycles. The mesenteries of the fourth cycle are small 

 and destitute of both muscle pennons and mesenterial filaments. 



In certain respects, such as the possession of a capitulum, this 

 form ditfers from the typical members of the genus ParacUs. It is not 

 improbable that it may be necessary to assign it to another genus 

 when the anatomical peculiarities of ParacUnia, Faranthus and 

 Parantheoides are more definitely determined. 



