2QO L. J. THOMAS. 



trimming the tentacles close to the bell margin with fine scissors 

 and then clipping this rim, with the velum included, free from the 

 remainder of the bell. Such preparations were stained with 

 borax carmine and mounted in damar. The otocysts, though 

 embedded in the mesoglea, were by this method sharply defined 

 and readily visible for accurate observations. In some speci- 

 mens prepared in this manner the finer details of structure could 

 be determined. By careful manipulation, mounts prepared in 

 this manner showed practically no distortion. Individuals 9 to 

 15 mm. in diameter were dehydrated, cleared, and mounted in 

 damar with a shrinkage of i mm. or less in diameter. This 

 shrinkage was obviously sustained uniformly by the various 

 tissues for no evidences of wrinkling or distortion of parts were 

 observable in the finished preparations. All drawings were made 

 with the camera lucida from prepared mounts and sections. 



STRUCTURE OF THE OTOCYST. 



Murbach (1903: 205) dismisses the anatomy of the otocysts 

 in Gonioncinus with the footnote: "The finer anatomy is natur- 

 ally omitted. The description of the nervous system and the 

 otocyst given in ' Das Nervensystem mid die Sinnesorgane der 

 Medusen,' O. u. R. Hertwig, text, pp. 48-69, Plates 4 and 5, fits 

 very nearly those of Gonioneinus." A careful examination of 

 the Hertwig descriptions and drawings of otocysts in other 

 genera reveals many points where a closer " fit " might be desired 

 if the descriptions and drawings are to cover the conditions found 

 in Gonioncinns. 



Superficial examination under a compound microscope reveals 

 the otocysts of Gonioncinns as tiny bubbles, each of which usually 

 encloses a single spherical object. This last mentioned body has 

 usually been considered as the otolith, though it probably com- 

 prises the entire sensory mechanism of the organ as indicated in 

 the introduction to this paper. Detailed structure of this body is 

 shown in Fig. 2, Plate I., which was drawn from a 15^ section. 

 This figure shows only the spheroid pendant from the wall of 

 the primary vesicle by the minute primary pedicel ( />/>) The 

 heavily nucleated cells which comprise the wall of the secondary 



