66 



On the Histology of Hydra fusca. [Dec. 18, 



For sections showing the cilia of the endoderm, the Hydrce were 

 kept for twenty-four hours in 1 per cent, osmic acid, then washed, 

 and preserved in weak glycerine until required for cutting. The 

 sections were cut by Dr. Pritchard's very convenient freezing micro- 

 tome, the specimens being placed in gum water before freezing. 



DESCRIPTION OP PLATE. 



Reference letters. 



ec, ectoderm. en., endoderm. 



m., middle layer. f., food particles. 



m. p., muscular processes. d., diatom included in an endoderm 



s. I., supporting lamella. cell. 



i. t., interstitial tissue. c, cilia. 



we., nematocysts. 



Figure 1. Longitudinal section of the body, distal end, (amnionic bichromate — 

 alcohol — eosin). The specimen was killed in full digestion, the endoderm 

 cells being gorged with food particles, amongst which is a diatom 

 frustule. The ectoderm and endoderm are unnaturally separated by the 

 action of the bichromate, and the supporting lamella is not shown. The 

 nuclei are not well shown; the specimen having been unfortunately 

 stained with eosin instead of carmine. 



Figure 2. Fragment of the supporting lamella, obtained by teasing, (osmic acid — 

 weak glycerine) . The wavy character of many of the adhering muscular 

 processes is well seen. 



Figure 3. Longitudinal section of the body, distal end, (osmic acid — weak glycerine), 

 showing particularly the flagella of the endoderm cells. The boundaries 

 of the ectoderm cells are not seen. 



Figure 4. Transverse section of the body, proximal end, (picric acid — alcohol — 

 carmine), showing the pseudopodia of the endoderm cells and the 

 included food particles, as also the absence of interstitial tissue and of 

 nematocysts in this region. 



Figure 5. Longitudinal section of a tentacle, (picric acid — alcohol — carmine). In 

 this section, selected as showing the food particles in the protoplasm of 

 the endoderm cells, no nematocysts, nor palpocils are to be seen. 



Figure 6. Longitudinal section of the -body, distal end, to show the typical structure 

 of the body wall. 



Figures 1 — 5 are accurately drawn, each from a single specimen, except for the fact 

 that the diatom d, in fig. 1, has been inserted from a similar, but otherwise 

 less favourable specimen. Fig. 6 is a combination of several preparations, 

 being the correct proportions retained. 

 All the figures were drawn with a Grundlach's -j^th immersion (for the use of 



which I am indebted to Professor Huxley) on Hartnack's small stand, and with his 



No. 3 eye-piece. 



The Society adjourned over the Christmas Recess to Thursday, 

 January 8, 1880. 



