Il6 H. H. NEWMAN. 



is less effective when it does begin. In last analysis the difference 

 is evidently to be expressed in terms of rate of change. The 

 whole process of ontogeny in these eggs is from the beginning 

 retarded, and the results are exactly similar to those which may 

 be obtained by the use of growth-retarding agents applied to newly 

 fertilised eggs. The first effect of pronounced retardation of the 

 normal growth process in the egg is the partial or complete 

 obliteration of the characteristic axes of polarity and symmetry 

 in the egg, a breaking down of the axial gradient. This results 

 subsequently in loss of unity of organization, involving physio- 

 logical isolation of blastomeres or of cell aggregates, in double 

 and triple polarity and consequent double or triple monsters, and 

 in a whole series of products of differential inhibition, such as 

 those described by Child for sea-urchin. 



8 10 1Z 



FIGS. 712. Later developmental stages in spontaneously parthenogenetic 

 eggs of Asterina. 7. The commonly occurring solid blastula type. 8. A pair 

 of twin blastube enclosed within one vitelline membrane, evidently the result 

 of physiological isolation of two blastomeres in the two-cell stage. o. A mul- 

 tipolar embryo gastrulating at several points. 10. Double monster with two 

 symmetrical archentera. //. Another double monster with an additional an- 

 terior archenteron. 12. A microcephalic ciliated larva, with differentiated 

 stomach and intestine, but no anterior parts. 



Some of the types of inhibited larvae found in cultures of spon- 

 taneously parthenogenetic Asterina eggs are shown and described 

 in figures 7-12. The solid blastula is the commonest type, a type 

 devoid of an axis of polarity (Fig. 7). Forms that are bipolar 



