Artificial Parthenogenesis m Starfish Eggs 381 



active about three or four hours after treatment with the acid- 

 ulated sea-water. The following record will illustrate : 



July 15, 1907, 12.37 p.m. Unfertilized sea-urchin eggs were placed in a mixture of 50 cc. sea-water 

 "*" 3 '-*-• TIT acetic acid; one portion (A) was transferred to normal sea-water after one minute, a second 

 (B) after i m. 30 s. At 4:30 p. m., lot A showed numerous irregularly shaped eggs in which 

 active amoeboid movement was in progress. In many eggs the movement was so energetic that the 

 actual contractions of the cell-surface and the protrusion of pseudopodia were plainly visible; many 

 even exhibited an active crawling or squirming movement, suggestive of sluggish muscular contractions. 

 In many eggs small portions of the surface protoplasm were constricted off- — small beadlike protuber- 

 ances like polar bodies being especially numerous. Transitions between irregular amoeboid masses and 

 distinct though irregular cleavage stages were not uncommon; the latter also showed continual and 

 active changes of form. Lot B showed essentially similar conditions. The temperature of the water in 

 the dishes was 25°. 



This observation seems interesting on account of the unusually 

 active nature of the amoeboid movements. The assumption of 

 irregular amoeboid forms by various eggs is familiar to most 

 experimentalists,^- and is especially frequent in starfish eggs. But 

 active crawling movements of the above kind have, so far as I am 

 aware, not hitherto been described in these eggs. The theoretical 

 interest of the phenomenon consists chiefly in the very clear indica- 

 tion which it affords that the form-changes in cleavage are of essen- 

 tially the same nature and due to the same conditions as are the 

 ordinary amoeboid movements of cells; these last, as may be inferred 

 from the closeness with which they may be artificially simulated, are 

 almost certainly due — at least as regards their main features — to 

 local (possibly electrically conditioned) changes of surface tension. 

 The above transitional condition between amoeboid movement and 

 cleavage supports strongly the view that the change of form in 

 normal cell-division is also due to surface-tension changes, which 

 diff'er from those causing amoeboid movements only in the very 

 regular and symmetrical distribution of the areas of lowered sur- 

 face tension. 



Experiments zvith Starfish Eggs 



A Conditions of Formation of Fertilization-membrane 



Exposure to temperatures of 45° and higher caused mature star- 

 fish eggs to become co"arse and opaque within 20 minutes or less. 



'^ Especially energetic amoeboid movements are seen in abnormally developing parthenogenetic eggs 

 of Chaetopterus; cf. F. R. Lillie, Archiv f. Entwicklungsmechanik, xiv, p. 487, 1902. 



