160 , CHARLES R. STOCKARD 



Tesuming a normal rate, the more rapidly developing parts still 

 maintain their necessaiy supremacy. 



On completely stopping development at a critical stage, that 

 is, when certain parts are progressing at excessive rates, as com- 

 pared with the rate in general, the rate of all parts is reduced to 

 zero or equality. On resuming development from such a con- 

 dition, the differential rates are not again established with suf- 

 ficient promptness and certain parts or organs are suppressed, 

 poorly expressed, or deformed in structure. On stopping devel- 

 ' opment at an indifferent stage, that is, when important inequali- 

 ties in developmental rate of the different parts are not occurring, 

 it matters not if the entire rate be reduced to zero. On resuming 

 development the parts all begin at about equal rates without the 

 necessity of a prompt establishment of differences and no par- 

 ticular arrests or suppressions occur. 



e. The types of arrests or deformities following a stop or slowing in 

 the rate of development 



Only a general statement of results from a few experiments 

 have been given in the previous pages without going into par- 

 ticulars regarding the variety of deformities occurring. At this 

 juncture I should like to enumerate in a very brief way the kinds 

 of abnormalities which have occurred in all of the experiments 

 where development has been stopped or slowed by a reduction 

 in temperature. 



In the first place, there were produced a nmnber of double- 

 headed, double-bodied, and twin individuals which will be fully 

 considered in the following section. Along with these were single 

 individuals with all varieties of eye defects, anophthalmia, micro- 

 phthalmia, monophthahnia, cyclopia, etc. These defects were 

 present in heads with either structurally normal or variously 

 malformed brains. The mouth and branchial arrangements were 

 frequently deformed. The otic vesicles were occasionally sup- 

 pressed to various degrees or developed abnormally during the 

 later stages. A number of specimens were short bodied, some 

 with bifed caudal ends. The general body form and the shape 



