MUSEUM OF COMPARATIVE ZOOLOGY. 26 



I was too early or too late for embryological material, although from 

 some indirect evidence drawn from what follows I am inclined to think 

 I was too early. 



The youngest stocks found I obtained in large numbers, and they 

 were of almost exactly tlie same age. Moreover, they agreed with the 

 youngest stages found by Leidy and figured by him ('84, Plate I. Figs. 

 5, 6, 7). I have represented some of these in Plate V. Figures 31, 32, 

 and, enlarged, in Plate II. Figure 15, and Plate V. Figure 46. 



I have already (pages 3-6) called attention to some of the characters of 

 the stalks of these young individuals. It remains to mention the " basal 

 plate " of such stocks. 



Unlike its condition in the adult, the " basd plate " is a relatively 

 large organ of elongated cylindrical form (Plate II. Fig. 15). Its outer 

 epithelium consists of sharply demarked cells, cuboidal above, columnar 

 below. This epithelium has given rise to a cuticula thin and dense 

 above, and thicker and less refractive below. The columnar cells are 

 somewhat less deeply stained than those at the end of the "basal plate" 

 farthest from the two stalks. Their nuclei lie at their inner ends. 

 The outer part of the cell contains spherical masses of granules. On the 

 whole, it stains less deeply than the inner end. Finally, one always 

 finds particles of dirt closely adherent to the under and lateral aspects 

 of the basal plate. 



These facts I interpret as follows. The columnar cells of the under 

 side are glandular, and secrete a sticky substance which causes the ad- 

 herence of the surrounding particles of dirt, and thus serves to anchor the 

 young stock. ^ The tissue of the interior of the "basal plate " is I'emark- 

 able, and difficult of interpretation from sections alone. In such sections 

 one sees bands running through the middle region and crossing at various 

 angles. Each of these " bands " is a nucleated cell, and probably repre- 

 sents a muscle fibre (cf. Plate V. Fig. 46). One sees also fibres having a 

 different appearance running radially from the base of the stalk to the 

 columnar cells of the " basal disc " over quite a long stretch (Plate II. 

 Fig. 15). In addition to these protoplasmic structures there are long 

 clear spaces which are bounded by thin membranes and contain occa- 



1 Seeliger ('90, p. 573) finds in Pedicellina a glandular differentiated zone on the 

 base of the stolon, where it conies in contact with foreign bodies. This, he says, 

 can be traced unbroken through the entire length, especially in young stocks, con- 

 sisting of few individuals. The foot gland of Loxosoma is an organ fulfilling a 

 function similar to that of the glandular cells of the stolon, but an homology of the 

 two organs can hardly be maintained. 



