ARTIFICIAL rARTHENOGENESIS AND FERTILISATION. 483 



pressure iu viirious other ways (Loeb). This may be 

 done by adding various inorganic salts to the sea water, 

 especially the salts of magnesium, potassium, sodium, and 

 calcium, in definite proportions (Loeb, Morgan, and others), 

 or by adding sugar or urea (Loeb). Other salts have also 

 given results, e.g. chloride of manganese (Dehige). The 

 effect is produced Avhen the eggs, after being left from 

 half an hour to two hours in the solution, are transferred to 

 pure sea water, and is due to the disturbance of the osmotic 

 pressure leading to loss of water by the egg, followed by 

 rehydration (Bataillon, Loeb, Giard, etc.), not to specific 

 chemical stimulation. 



The nuclear activity may also be roused by other chemical 

 bodies, as strychnine (Hertwigs, Morgan), chloroform, ether, 

 alcohol, by lack of oxygen (Mathews), by very dilute hydro- 

 chloric acid (Loeb, Delage). 



Further, purely physical agents may have the same effect — 

 heat (Mathews, Bataillon, Delage, Viguier), cold (Morgan, 

 Greeley), and, most important, agitation (Mathews). Mathews 

 had previously proved for Asterias, and Morgan for Arbacia 

 also, that shaking of unripe eggs caused them to form the 

 polar bodies — the shaking presumably causing dissolution of 

 the nuclear membrane. Eipe eggs of Asterias, but not of sea- 

 urchin, act in the same way, but only after they have lain 

 some time in water ; after two hours larva3 begin to appear 

 on shaking; after four liours, hard shaking produces a large 

 proportion of larvse, and the mere transference of the eggs 

 by a pipette from one vessel to another is sufficient to form a 

 few larvEG. A few hours later the slight amount of shock 

 experienced in the transference of tlie eggs, causes a large 

 number to begin to develop, though they do not go beyond 

 the late segmentation stages. At this time shaking causes 

 all to develop, but none roach the blastula stnge. Loeb and 

 Fischer have extended this observation to the Annelids, 

 Cha^topterus and Amphitrite. 



The mitotic phenomena produced artificially are apt to be 

 irregular, and the division of the cell body is often unecpial 



