452 Froceedi7igs of the Royal Physical Society. 



of moisture (49, 59). The degree of moisture has a marked 

 effect ou the growth of the mantle of molluscs. The well- 

 known case of the transition from Axolotl to Amblystoma 

 (67) may be recorded under this head. 



(c.) Composition of the Medium. — In spite of certain 

 strictures (37, 38), the classic experiments of Schmankewitsch 

 (GO) are still accepted to this extent at least, that by altering 

 the salinity of the water he was able gradually to change 

 one species of Artemia into another. There are numerous 

 experiments on record as to the effect of transferring organisms 

 from one medium to another (35, 40, 55, 56, 58, 65, 66), and 

 Sollas's observations (63) on the origin of fresh- water fauna 

 are in this connection of great interest. Alteration of salinity 

 lias been shown to influence form (61), rate of development 

 (69), colour (60), and even affects the characters of the blood- 

 corpuscles (40), etc. The elaborate researches of Fredericq 

 (43, 44) are in this connection of great importance, as show- 

 ing that the composition of the blood of many animals under- 

 goes change with alteration of salinity. Krukenberg (50) 

 has also recently made a long series of observations on the 

 relation of the composition of Medusoe to that of the surround- 

 ing medium. Very fundamental are the elaborate researches 

 of Frommann (45) on the reactions of protoplasm and cells 

 to external chemical influences. Zacharias (70) made sperms 

 pass from a cylindrical to a pseudopodic, and thence to an 

 active motile phase ; Geddes (45a) refers to the simple 

 experiment of bringing an Actinosphcerium down to an 

 amoeboid level by the addition of a drop or two of dilute 

 ammonium carbonate ; and the Hertwigs have made a wide 

 series of observations (48) on the influence of chemicals on 

 ova, fertilisation, segmentation, and cell-division. Lastly, 

 some curious observations (39, 64) on artificial parthenogenesis 

 by chemical stimulus may be noticed. 



(d.) Food (71-111). — Zopf (111) notices in his monograph 

 on Monadina that a surplus of food caused ciliated forms to 

 become, as one would expect, amoeboid (more anabolic), while 

 a larger overplus was followed in amoeboid phases by still 

 greater passivity. That abundant nutrition is one of the 

 conditions of the passivity of parasites (94) seems evident. 



