Sharp: Diplodinium ecaudatum 63 



THE ECTOPLASMIC STRUCTURES 



Cuticle. The thin but resistant cuticle covers the entire body 

 and is so highly specialized over certain regions (sk. a., pi. 3, figs. 1-2) 

 as to demand special description. There are three such regions over 

 which the cuticle shows a well-defined differentiation. (1) Over the 

 dorsal (D.) and left surfaces of the body the cuticle is comparatively 

 smooth, giving only faint evidence of longitudinal striations and in 

 places traces of mottling. (2) The cuticle over the ventral surface 

 (V.), extending from the middle to the posterior extremity of the 

 body and over the spines when present, is faintly but distinctly mot- 

 tled. This mottling is caused by minute diamond-shaped depressions 

 in the cuticle which at certain levels do not transmit the light as 

 readily as the non-depressed portions, and hence appear as little 

 shadows. (3) The third region, embracing the anterior one-half of 

 the left ventral and ventral surfaces and the anterior two-thirds of 

 the right surface, is divided into three well-defined areas by under- 

 lying ectoplasmic structures which appear to be skeletal in function. 

 Eberlein (1895, p. 240) says in his description of Ophryoscolex iner- 

 mis: "Die Ran der der Bauchflache sind beiderseits durch einen 

 Streifen starker granulierten Plasmas begrenzt (fig. 1)," but makes 

 no mention of a definite underlying structure. Erlanger (1890, p. 

 654) observed, in Chlamydodon mnemosyne Stein, a strange "Band" 

 situated between the dorsal and ventral surfaces, surrounding the 

 entire body with the exception of a small interruption at the posterior 

 end, and which was clearly marked off by cross striations. And 

 Levander (1894, pp. 66-67) in his description of Plagiopyla nasuta 

 Stein calls attention to a previously unnoticed cross-striped band of 

 differentiated ectoplasm situated on the right side of the body near 

 to and parallel with the ventral border. 



The above-mentioned cases of ectoplasmic differentiation might 

 be conceived as being similar to the peculiar ectoplasmic differentia- 

 tions which are described in this paper as skeletal areas. In none 

 of the above cases, however, is anything said about a specially differ- 

 entiated underlying ectoplasmic structure. 



To GHinther (1899) belongs the credit for being the first to note 

 and describe this underlying ectoplasmic structure. He says (p. 

 553) : "An jedem Ophryoscolex caudatus, schon bei der Untersuch- 

 ung des lebenden Thiers, besser natiirlich an Konservirten gefarbten 

 Thieren und Schnitten derselben, habe ich ein Organ (cf. figs. 1, 2, 5, 

 6, 7 st\) gefunden, im Ectoplasma liegend, iiber das bis jetzt noch kein 



