4 BULLETIN OF THE 



Au optical longitudinal section of the living stalk (Plate I. P^ig. 7) 

 shows that it consists of a thick cuticula, within which is a mass of ill- 

 delined tissue. The cuticula is thicker and more opaque in the basal 

 segments, thinner and more transparent in the distal ones. Each of the 

 basal segments often contains a mass of globular, highly refractive bodies, 

 which may be forced out from the segment by crushing the latter (Plate 

 I. Figs. 4, 5). Isolated by this means they are seen to be of the most 

 varied size, and to resemble yolk spherules. Besides these granules, one 

 finds lying near the cuticula in all but the oldest segments a fibrillated 

 layer consisting of elongated, spindle-shaped, highly granular cells in the 

 midst of the yolk spherules (Plate I. Fig. 7), and, finally, one or several 

 flickering bodies reminding one by their motion of the cirri^ of flame 

 cells. lu the dark zones optical sections reveal indications of a transverse 

 septum. 



A more accurate insight into the histological structures is gained 

 from thin sections of the stalk. 



The cuticula appears in two conditions, which are not sharply separated, 

 but pass into each other through intermediate conditions. The one 

 kind (Plate I. Fig. 4, eta.) occurs in the middle zone of each segment. 

 It is transparent and flexible, and becomes thicker in passing from the 

 distal to the proximal segments. It stains in hsematoxylin, and is then 

 seen to be composed of laminae, for it appears in section distinctly 

 striated (Plate I. Fig. 4 ; Plate II. Fig. 16). The other kind of cuticula 

 occurs chiefly at the constrictions between segments, but it extends over 

 the two ends of the segments also, and even over the middle zones of 

 the segments, as an outer cuticula (Plate II. Fig. 8, ctaK). It forms, 

 moreover, the septa between adjacent segments. It does not stain in 

 hsematoxylin, is more highly refractive than the first kind, and has a 

 yellowish color by transmitted light. Where it passes over into the first 

 mentioned kind of cuticula, it becomes distinctly striated, and gradually 

 loses its specific characters, gaining those of the first kind, of which it is 

 probably only a modification. It is the presence of these two kinds of 

 cuticula that causes the superficial appearance of alternating light and 

 dark zones on the stem. These two kinds of cuticula do not correspond 

 to the inner and outer cuticulas which Ehlers ('90, pp. 16, 17) describes 

 for Ascopodaria. Two layers with the characters of those of Ehlers ap- 

 pear not to exist in Urnatella. 



The ectoderm (Plate II. Figs. 11, 10, 16) diminishes in thickness from 



1 I employ the word " cirrus " in the sense in which it is used by Biitschli 

 for Ciliata (cf. Bronn's Thierreich, Protozoa, p. 1324). 



