Artificial Parthenogenesis in Starfish Eggs 391 



cytoplasm possesses a certain formative capacity of its own;^^ this 

 under the above abnormal conditions may give rise to structures 

 having very definite peculiarities, but quite foreign to the normal 

 development. 



Under favorable conditions a large proportion of eggs undergo 

 regular cleavage and development. The following series (Table 

 II) will illustrate; the eggs (all from a single lot) were exposed to 

 temperatures of 35°, 36°, 37° and 38°, for varying brief periods 

 during the early maturation period (between 20 and 45 minutes 

 after removal from the animal, before separation of the first 

 polar body). The susceptibility varies somewhat within this 

 period; but, as will be shown later, warming may produce develop- 

 ment at any time between the dissolution of the germinal vesicle 

 and the formation of the first polar body (after which time it 

 becomes increasingly difficult to incite development by this means). 

 Within at least the greater part of the period of exposure covered 

 by this series the susceptibility to development by warming varies 

 relatively shghtly, and the condition of the eggs may be regarded 

 as essentially uniform throughout. Later experiments will be 

 described in which the variation in susceptibility at diflPerent 

 periods during maturation is itself made the subject of study (cf. pp. 

 396, et seq.) 



Eggs from the same lot were treated in a precisely similar 

 manner on the afternoon of the same day, from 2.36 to 3.06 p.m. 

 All had matured in the typical manner. The result was quite 

 different. Membrane-formation was less uniform and required 

 a more prolonged exposure to the respective temperatures, and 

 although in favorable experiments a considerable proportion of 

 eggs underwent cleavage, mostly irregular, not a single swimming 

 larva was obtained. This kind of experience has been uniform. 

 Ihave neversucceeded,afterthe completion of maturation, in bring- 

 ing unfertihzed eggs to the free-swimming stage. The eggs invari- 

 ably either fail to cleave, or cleave more or less irregularly, usually 

 after undergoing rregular form-changes, and die at an early stage. 



1' Compare Wilson's account of the phenomena in the isolated enucleated polar lobe of Dentalium; 

 cf. also the references in his paper to analogous phenomena in echinoderm eggs. Wilson: Journal of 

 Experimental Zoology, vol. i, p. 53, 1904. 



