OPPENIIEIMER. — RIIYNCHOBOLUS DIBRANCHIATUS. 557 



the parapodial pouch." Whatever may be the condition in the case of 

 the gills, the furrows of the papillae do not encircle those organs, for I 

 have found that they exist on the posterior face of the papilla only. 

 That the function of the furrows of the papillae is similar to that sug- 

 gested by Ehlers for those of the gills, namely to determine the place of 

 folding when the organs are retracted, may well be questioned, for there 

 is no evidence that the papillae are ever retracted ; there are no muscles 

 to effect contraction, nor have I ever found the organs in a retracted 

 condition. 



The papillae have been studied in sections fixed in a mixture of 

 corrosive sublimate and acetic acid and subsequently stained in Klein- 

 enberg's haematoxylin ; in sections fixed in corrosive sublimate and 

 stained iu iron haematoxylin ; in preparations fixed in vom Rath's 

 ('95, p. 282) picric-osmic-platinic chloride-acetic mixture (to which tap- 

 water was sometimes added) ; and in methylen-blue preparations. The 

 sections stained in iron haematoxylin I prepared, through the kindness 

 of Professor Lloyd, in the laboratory of the Teachers College, Columbia 

 University. 



The living substance of the papillae appears to consist of either four 

 or five cells, which are, to judge from the nuclei, of two kinds. Two of 

 the nuclei (PI. 1, Fig. 3 ; PI. 3, Fig. 16, nl. ba.) found in the papillae are 

 basal in position and larger than the others ; the remaining two or three 

 (ill. ax.) are nearer the apex of the papilla and also usually more nearly 

 axial in position (PL 1, P'igs. 3, 4 ; PI. 2, Figs. 9a, 9b, 1 1 ; PI. 3, 

 Figs. 1G, 17 ; PI. 4, Figs. 2G, 28, 30). The boundaries of the two cells 

 to which the two basal nuclei belong cannot be made out by any process 

 that I have employed. 



In preparations made with vom Rath's mixture, the protoplasmic con- 

 tents of the papilla are distinctly vacuolated. The vacuoles are also seen 

 with nearly equal distinctness in the methylen-blue preparations, but not 

 quite so clearly in sections stained with iron haematoxylin or with Kleinen- 

 berg's haematoxylin. The vacuoles are merely clearer, usually roundish, 

 regions, which stand out distinctly, in contrast to the deeply stained granu- 

 lar or fibrous surrounding substance, and are quite variable in size, as is 

 to be seen in PI. 3, Figs. 18, 20; PI. 4, Figs. 22, 25, 29. I believe 

 that some of the more elongated vacuoles and the clusters of the 

 more rounded ones in the region of the central nuclei (Figs. 22, 29), 

 and perhaps a lighter coloring of the axial region of the papilla (PI. 1, 

 Fig. 4 ; PI. 2, Fig. 11), gave rise to the following opinion expressed by 

 Ehlers (p. 679) : " There lies under the chitinous covering a thin sheet 



