LOW TJiMPERATURE — DEVELOPMENT OF FUNDULUS 459 



largely though not wlioliy non-cellular masses occasionally gave 

 rise to true embryos exhibiting the usual developmental proc- 

 esses. Such embryos usually showed various degrees and kinds 

 of abnormalit3% but some few ultimately produced normally 

 hatching larvae. These masses were therefore more than merely 

 hving; their later history shows that even in that state there 

 must have remained present, in many instances, some kind or 

 remnant of an underlying construction or organization that 

 determined either directly or through some regulatory process, 

 development of parts, at least, of Teleost embryos, and in a few 

 instances of essentially normal Fundulus embryos. 



My chief object in describing, at this time, the effects of low 

 temperature upon the development of Fundulus is not to give 

 a morphological or histological description of the malforma- 

 tions and abnormalities produced, but to suggest the bearings of 

 these results upon certain cuiTent hypotheses as to the real 

 causes of such defects and the way in which the unusual physi- 

 cal conditions may have affected the morphogenetic properties of 

 the ovum. I shall not attempt to review extensively the various 

 suggestions as to the causes of monstrous development, but 

 some of the more recent hypotheses only may be examined from 

 the point of view of the results described here. For this pur- 

 pose I shall refer chiefly to the suggestions made by tliree recent 

 workers in this field. 



As a preliminary word I should note that such observations as 

 these show that ''the idea that the low temperature only re- 

 tards the chemical reactions underlying development." (Loeb 

 '15, p. 59) is, for the Fundulus egg, true only to a certain point.- 

 When temperatures are lowered below say 12-14° C. the orderly 

 developmental processes are not only slowed but may be actu- 

 ally modified so that some of the consequent processes are ren- 

 dered abnormal. This may, of course, be due primarily to the 

 fact that certain processes are slowed more than others, but the 

 result is a disturbance of normal development which is different 

 from a mere slowing down of the entire mechanism, the com- 

 ponent processes remaining normally related to one another. 

 Apparently the precise temperature when this effect is produced 



