EARLY DEVELOPMENT IN THE FROG. 339 



varies from nearly normal (in the less inhibited ones) to 10/10 

 (more inhibited ones). In the more extreme inhibitions some 

 cases of secondary invaginations are seen and a decrease in the 

 gastrular angle is characteristic. Almost any type may be pro- 

 duced at will simply by varying the concentration of the in- 

 hibiting agent, or the length of the exposure, or the stage at which 

 the egg is introduced into the experiment, or by varying several 

 of the factors at once. The chief limiting factor in the control 

 of these and other modifications is the variation in susceptibility 

 exhibited by the eggs of different females. Several preliminary 

 attempts may be necessary before the desired result is obtained. 

 Some of the experiment? are cited below, in which these modifica- 

 tions were prominent, and'which serve to illustrate a few of the 

 many different ways in which these abnormalities may be pro- 

 duced. 



Experiment IV 21. l Unsegmented eggs, introduced into 



FIG. 17. Inhibition of both dorsal and lateral lip regions of the blastophore, 

 resulting in a "flat-crescent" blastopore. 28 1/2 hours' exposure to w/io.62 LiCl 

 from unsegmented stage. (Exp. IV 22.) 



m/7 LiCl I 1/2 hours after fertilization. After 21 hours in LiCl 

 and 7 hours in water a few of the eggs showed a slight equatorial 

 wrinkling but no distinct blastopore was present. After 24 hours 

 in LiCl, and 24 hours in water most of the eggs were in late 

 blastula stages in which the segmentation cavity was completely 

 lined with one or more layers of small round slightly pigmented 

 cells. 



Experiment IV 21. After 20 hours in m/8.$ LiCl and 8 hours 



1 Eggs used in experiments IV 21, 22, 26, 27, 29, 31, 33, 34, all came from the 

 same female, and were introduced into the different experiments 11/2 hours after 

 deposition. 



