KOFOID : CRASPEDOTELLA. 165 



somewhat denser mass of plasma not far from the nucleus. Its walls 

 are coarsely striate, with a few prominent longitudinal ridges. Its 

 opening is unquestionably within the bell and most careful scrutiny 

 reveals no orifice on the outer surface. 



In LeptodiscKS Hertwig describes the cytopharynx (Cytostom) as 

 opening upon the upper (outer) surface of the curved disk on the same 

 face as the flagellar sheath. In Craspedotella it unquestionably opens 

 within the bell on the opposite face from the flagellar sheath. This 

 seems to afford an additional ground for the generic distinctness of 

 these two forms. The two organisms also diverge in other details 

 of structure. In Leptodiscus the granular plasma is of small extent and 

 very slightly protuberant, the pharyngeal striae are fine and close set, 

 the cytopyge does not appear, the vacuole is small, and the peripheral 

 plasma has less of a radial arrangement. 



Adaptation to a pelagic life in the oceanic environment has resulted 

 in the case of Leptodiscus, and still more in Craspedotella, in the devel- 

 opment of a bodily form which bears a most striking resemblance to 

 that attained by another and much higher group of organisms living 

 under the same conditions. In Craspedotella there is diflferetitiated 

 even a superficial organ, the velum, with the accompanying bell-cavity, 

 with form, relations, and possibly a function, similar to those of the 

 corresponding organ in the medusa. The necessities of flotation and 

 locomotion have brought about independently in the medusa and the 

 cystoflagellate an external similarity in form, though the inner struc- 

 tural elements are exceedingly diverse in the two, and the one is a 

 unicellular and the other multicellular organism, — an instance of 

 convergence of the most striking character. 



