326 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



think that this peculiar curved position is one often 

 assumed in life. On closer examination this conviction is 

 strengthened, for the surface of both stalk and calyx is 

 found to be differentiated into two regions, a spiny and a 

 spineless one. The latter occupies a narrow strip extending 

 from the base of the tentacles on the cesophageal side down- 

 ward over the stalk to the stolon (figs, i and 2, sfl. reg.). 

 That this region possesses greater muscular power is 

 apparent from a very casual examination of a glycerine 

 mounted specimen. Figure 2 represents such a prepara- 

 tion. Here, in order to show the direction of the muscle 

 fibers, the stalk is drawn in optical section. The spineless 

 region {spl. reg.) and the longitudinal muscle fibers are 

 seen to be on the same side. 



Topographically, therefore, the surface of the polypide 

 is divided into a ventral and a dorsal side. That part of 

 stalk and calyx which possesses greater muscularity and 

 which is free of spines is the ventral side; the spiny region 

 is the dorsal. Throughout this description the terms ven- 

 tral and dorsal, applied to both stem and calyx, will be 

 used with this signification. Furthermore, although as we 

 shall see, the connection between stalk and calyx is inti- 

 mate, yet for purposes of description I will distinguish 

 between them, and I will first describe the calyx. 



(a). The Calyx. — The cuticle over the spiny region is 

 thickened in places into ridges or ribs, upon which spines 

 develop at regular intervals, although they are not lacking 

 in other parts. One of these ridges is especially conspicu- 

 ous, forming an almost circular rib at the base of the tenta- 

 cles (fig. I, ten. r.). It is thickened at the summit (fig. i, 

 sum.) of the tentacular disc and gradually grows more slen- 

 der as it approaches the spineless region on the ventral 

 side. Upon it six or eight spines are developed, forming a 

 sort of coronet around the face, so to speak. From the 

 summit of the calyx in the sagittal plane, a short, chitinous 

 thickening of the cuticle extends forward upon the tentac- 

 ular disc (fig. I, sag. r.) This also bears one or more 

 spines. Dorsally, in the sagittal plane, a double row of 



