318 Prof. Allman on the Structure and 



filled with opaque brown granules. Where the encloderm 

 passes into the tentacles it loses its large-clear-celled condi- 

 tion, and consists of small round cells so loaded with opaque 

 granules that the axis of the tentacle appears nearly white 

 under reflected light. 



4. The free surface of the endoderm carries long, very 

 slender, sluggishly vibrating cilia, and is overlaid with a thin 

 layer of transparent homogeneous protoplasm, which on the 

 villus-like processes becomes especially distinct, and which 

 develops minute mutable pseudopodia which are being con- 

 stantly projected and withdrawn. Indeed the vibratile cilia 

 appear to be but a modification of these pseudopodia! processes 

 of protoplasm. 



5. Interposed between the endoderm and the ectoderm is 

 the fibrillated layer. It is extremely well developed, and 

 consists of longitudinal muscular fibrillar, closely adherent to 

 the outer surface of a structureless hyaline membrane — the 

 " Stiitzlamelle " of Beichert. The fibrillated layer, with its 

 supporting membrane, is so strong as to remain entire in a 

 section of the animal after the tissues on both sides of it have 

 been broken down. 



6. The ectoderm is composed mainly of two or three layers 

 of small round cells containing yellowish granules. Among 

 these cells the thread-cells may be seen, lying chiefly near 

 the outer surface of the body. Two forms of thread-cells 

 may be here distinguished — one ovate with the invaginated 

 tube occupying the axis, the other fusiform with the in- 

 vaginated tube oblique. The whole free surface of the ecto- 

 derm is overlaid with an exceedingly thin, transparent and 

 structureless pellicle. 



7. The deeper part of the ectoderm consists of a veiy 

 remarkable tissue composed of peculiar membraneless cells, 

 each of which is prolonged into a long fine process which can 

 be directly traced into the fibrillated layer. I am thus enabled 

 so far to confirm the observations of Kleinenberg on cells of 

 apparently the same significance in Hydra. In Myriothela, 

 however, these caudate cells do not, as in Hydra, reach the 

 surface. They form a deep zone interposed between the mus- 

 cular layer and the superficial layer of the ectoderm. Though 

 the caudate cells are in intimate association with the fibrillated 

 layer, I did not succeed in tracing a direct continuity of the 

 individual fibrillar with the processes of the cells as described 

 by Kleinenberg in Hydra. While the deep zone may, in 

 accordance with Kleinenberg's views of the caudate cells in 

 Hydra, be regarded as a nervous layer, the superficial zone of 

 the ectoderm will represent an epidermis. 



