298 L. J. THOMAS. 



EXPLANATION OF PLATE. 

 SYMBOLS. 



c, cavity of secondary vesicle, p p, primary pedicel, 



e c, ectoderm, r, ring canal, 



e ii, endoderm, s, spheroid, 



e x, exumbrella, s I, supporting layer, 



m, mesoglea, ^ p, secondary pedicel, 



n, nerve ring, s 11 , subumbrella, 



n c, nettling cells, j v, secondary vesicle, 



o, otolith, 7', velum. 



PLATE I. 



The otocyst of Gonionemus rertens. All drawings were made with the 

 camera lucida. The projected scale indicating magnification in each instance 

 has the value of o.oi mm. 



FIG. i. Section through bell margin showing general location of the 

 otocyst within the mesoglea and its orientation with reference to ring canal. 



FIG. 2. Longitudinal section through the spheroid of an otocyst showing 

 histological details. 



FIG. 3. Tangential slice from the wall of the spheroid similar to the sec- 

 tion removed from the front surface of the wall of the secondary vesicle in 

 the foregoing figure. 



FIG. 4. Longitudinal section through an otocyst to show the concentric 

 rings within the otolith. 



FIG. 5. A spheroid with a portion of the wall of the secondary vesicle 

 removed. 



