8oo BIOPHYSICAL PHENOMENA [pt. iii 



that in the early stages of Bimastus the three micromeres acted as 

 osmoregulators for the rest of the embryo by excreting water, but 

 that this was not so in Eisenia, and when he came to estimate the 

 osmotic pressure of the milky liquids in the cocoons he found that the 

 two were indeed different. The cocoon liquid of Bimastus gave a 

 freezing-point depression of— o-o6° corresponding to 0-78 atmosphere 

 or o-io8 per cent, sodium chloride, while that of^ Eisenia gave one 

 of — 0*39° corresponding to 4-8 atmospheres or o-68 per cent, sodium 

 chloride. Svetlov found that the cocoon shells, although hard, were 

 not impermeable, and showed, in fact, the properties of semiperme- 

 able membranes. Taking then samples of liquid from the normal 

 habitat of the two worms, humus earth infusion for Bimastus and 

 dunghill infusion for Eisenia, he found that the former was much 

 less concentrated than the latter, the relation being the same as that 

 found between the milky contents in the two cases. Svetlov con- 

 structed micro-osmometers with the cocoons from the two species 

 and found that the permeability of Bimastus was not quite double 

 that of Eisenia. Although the process was complicated in Eisenia, 

 cocoons (of both species) placed in solutions of known osmotic 

 pressure would come gradually into osmotic equilibrium with them. 

 The osmotic pressure of the cell-interior of the eggs themselves was 

 probably alike in both cases as the osmotic pressure of the adult 

 blood was the same, and therefore, Eisenia, having, according to 

 Svetlov's view, either abandoned or never evolved the osmoregulator 

 micromeres of Bimastus, has to lay its eggs in the dungheap liquid 

 or " Mistfliissigkeit " which has a high osmotic pressure. 



The osmotic relations of the eggs of nematode worms have only 

 once been investigated — by Szwejkovska. Between fertilisation and 

 the first cleavage there occurs, she found, a great diminution in the 

 size of the egg-cell while the egg as a whole remains unaltered in 

 size. The egg swells only slightly in hypotonic solutions. By the 

 plasmolysis method, she found the freezing-point depression of the 

 egg-interior to be - 0-599° in the unfertiHsed egg, - 0-629° in the 

 fertihsed egg before the eHmination of the first polar body, and 

 — 0-636° after the elimination of the first polar body. 



A great deal of work has been done on the permeabiUty and osmotic 

 pressure of echinoderm eggs. The jellies surrounding them when 

 unfertiHsed, and which can be made visible by the Indian ink method, 

 have been found to take up salt from the water. Glaser noticed 



