INITIATION OF DEVELOPMENT IN CH/ETOPTERUS. 23 



metaphase of the first maturation spindle, the second the extru- 

 sion of the first polar body, the third the completion of matura- 

 tion, the fourth is cleavage (the second, third and fourth may be 

 omitted), the fifth shows varying degrees of differentiation up to 

 the formation of swimming larvae of greater or less activity. A 

 graded series of stimuli may be determined in which the develop- 

 ment may be made to stop at almost any step in the process. 

 The chief difficulty in the artificial parthenogenesis has been 

 to induce cleavage. Formerly all successful efforts to induce 

 parthenogenesis in Chcetoptenis resulted in the production of un- 

 segmented larvae only. 1 One of my principal objects has been to 

 discover, if possible, something of the conditions determining 

 cleavage. I have found many agents that will induce the de- 

 velopment of swimming larvae without cleavage, but only two 

 thus far which led to the production of segmented larvae, (i) 

 subjecting the eggs to the action of heat, and (2) the use of 

 oxygen-saturated sea-water after a short exposure of the eggs to 

 a potassium chloride solution. The latter gave segmented 

 larvae in so few cases that I consider the results as somewhat 

 uncertain. Of the heat results there is no doubt. The fact 

 that so many fertilized eggs develop without cleavage suggests 

 that any abnormal condition is likely to have as a result the 

 suppression of cleavage,- that the balance of developmental 

 phenomena is a delicate one. The variety of agents that will 

 induce development of some sort indicates that the egg is in a 

 rather easily disturbed equilibrium, a very labile condition. 



1 Since sending this paper to the BULLETIN I have read the account by Professor 

 Jacques Loeb and Dr. Hardolph Wasteneys, "Fertilization of the Eggs of Various 

 Invertebrates by Ox-Serum," published in Science, Vol. 36, No. 921. 1912. In this 

 paper they announce the production of cleavage in unfertilized eggs of Chalop- 

 terus by the following method. "We induced segmentation in the eggs of Chce- 

 topte.ms by putting them for from iH to 2 H minutes in a mixture of 25 c.c. % M 

 strontium chloride + 25 c.c. M/2 NaCl + CaCl + KC1, then for ten minutes 

 into ox-serum diluted with its own volume of the above mentioned solution and 

 then by putting them for thirty minutes into hypertonic sea-water." The par- 

 thenogenetic agent is considered to be the lysin in the ox-serum, and the authors' 

 conclusion is for Chcetopterus as for the sea-urchin, that the first phase of fertili- 

 zation consists in a superficial cytolysis. 



