Pom-jiia Collesjie, ClarcnKint. California 51 



floor of the diaphragm. It is elongated transversely, the two 

 rounded ends being composed of a surface layer of cells with deeper 

 fibers. Some of the fibers form a commissure. From each end of 

 the brain two bundles are given off; one on each side passes to the 

 lophophore. Sonsory bristles were seen from the tentacles. Dorsal 

 sense organs as described in other forms are absent in this. 



Stiasny, 1905, shows the ganglion of PediceUina but with no 

 detail. Retzius, 1905, shows the sensory nerves in the surface of 

 PediceUina. These sensory cells bear bristles and are connected 

 with nerve strands which form a wide network of fibers. Sensory 

 cells were found in the tentacles. 



Assheton, 1912, found the nervous system in two species of 

 Loxosoma. The branches are figured and sense cells are mentioned 

 on the hypostome, lophophore and tentacles. 



I have been able to study the reactions of two Pacific coast 

 species of endoproctans. In Barentsia gracilis Hincks, the condi- 

 tions are much as in PediceUina. The ganglion is small and in the 

 usual position. The animals are colonial with narrow strands con- 

 necting the individual members of the colony ; the muscular bases 

 of each individual cause them to rotate in an active manner. Gen- 

 eral conditions in Myosoma spinosa Robertson are similar except 

 that the whole stem is flexible. In Barentsia the polype at the 

 end of the stem is movable at its stalk. The ganglion is much as 

 Nitsche describes. There is some indication of sense cells as shown 

 by Harmer as demonstrated by the methylene blue method although 

 I never obtained a perfect picture. The tip of the stem is slightly 

 smaller where it joins the body of the individual and methylene blue 

 shows bipolar cells at this point. Along the stem there are sensory 

 pits which are the only breaks in the strong chitin-like covering of 

 the ten elongated cells of the stem. In Myosoma, in place of the 

 pits on the skin there are well developed hollow hairs much like 

 those of arthropods. 



Tactile or other stimuli may cause a rotation of the stems with- 

 out a contraction of the tentacles, but severe stimuli will also cause 

 the tentacles to contract. Stems with their tips cut from the body 

 continue to rotate when stimulated. Movements of the body 

 of the polype on the stems may be caused by tactile stimuli. The 

 eff"ects of stimulation may be carried from one polype to another 

 through the connecting stems. One polype in line with others 

 may be fatigued so that it will not carry the stimuli to others. 



The stems and bases of both species seem capable of exciting 

 movements of the individual as a whole better than the tentacles or 

 body. In the rotating movements the tentacles are not often re- 

 tracted unless the stimulus is very severe or the tentacles them- 

 selves are touched. 



The control of movements of the tentacles and body are prob- 

 ably centered in the ganglion. The excitation to the rotation of 



