686 PROCEEDINGS OP THE ACADExMY OF [DeC, 



cilia and the complete absence of the interstitial connective tissue 

 cells. In a horizontal section of the ciliated pit the contrast 

 between the three regions is very marked. In a preparation 

 stained with hiematoxylin eosin, the outer and inner regions are 

 studded with the deep-blue nuclei of the connective tissue cells, 

 while the median region appears pink, from the cytoplasm of the 

 supporting cells, their small nuclei being very inconspicuous. 



The epithelium of the ciliated canal is a one-celled layer. The 

 cells are much lower and wider than those of the pit and bear 

 shorter cilia. 



The anterior part of the cerebral organ proper, fig. 21, right 

 side, is richly provided with gland cells, GL-^. These are large 

 pear-shaped bodies with long slender ducts that open into the 

 ciliated canal. The cytoplasm is abundant, especially at the base 

 of the cell where the large spherical nucleus is situated. The 

 secretion is homogeneous and stains red, hrematoxylin-eosin stain. 



The posterior part of the cerebral organ, fig. 21, left side, con- 

 tains other gland cells of a different character, Gl.^. The cyto- 

 plasm is inconspicuous, the nucleus is small, and the secretion has 

 the form of large globules that stain a faint bluish-gray. These 

 cells are prominent in life, evidently containing oily globules. 



The cerebral organs are well supplied with nervous substance. 

 Ganglion cells of the first type, fig. 21, G. Cu ^^^ very numerous. 



b. The Lateral Grooves. — The lateral grooves are two shallow 

 elongated pits extending horizontally, one on each side of the 

 body, above the lateral nerve chords. Each has a length of about 

 1.5 mm. 



The grooves are constant in position in the different specimens 

 examined, always beginning at the posterior end of the glandular 

 zone, Diagram 1, Gl.Z. and L.G., and ending about 1.5 mm. in 

 front of the great thickening of the inner circular muscle and the 

 beginning of the middle intestine. 



The lateral grooves are distinctly seen in cross sections of this 

 region of the body, appearing as small pits or depressions in the 

 epithelium external to each lateral nerve chord, but they are not 

 macroscopically distinguishable in cither living or preserved speci- 

 mens, although they have been repeatedly sought. The shallowness 

 of the grooves has probably rendered them indistinguishable 

 except by the microscope. 



