EFFECT OF EXTRACTS UPON DEVELOPING EGGS. 93 



of these were slight : others were more evident, as, for example, 

 the exogastrulae, noted in Table II. Their appearance may indi- 

 cate an arrest of development at the gastrula stage or earlier; in 

 fact, it was noticed that in most cases only after the larvae had 

 remained for a day at the gastrula stage, did the exogastrulae 

 appear. Some exogastrulae, however, appeared after a slowing 

 up of development from the blastula into the gastrula. The 

 further records of experiments planned may render a more definite 

 position on this point possible. 



As far as temperature was concerned in carrying out these ex- 

 periments, it would seem that the comparatively small variation 

 from day to day noted above in the discussion of methods, would 

 scarcely be sufficient to cause the development of abnormal types. 

 And furthermore, if by any chance slight changes in the tempera- 

 ture from day to day might have resulted in the development of 

 abnormalities, these abnormalities should be present in the controls 

 in as great numbers as in the extract cultures. Such was not the 

 case in the investigations outlined in this report. 



In considering the part which the extract may have played in 

 altering the normal oxidations in the developing eggs, three pos- 

 sibilities are evident : the rate of oxidation may be increased in 

 which case it would seem more probable that there would be an 

 acceleration rather than a retardation in the rate of development, 

 or the rate of oxidation may be decreased by the action of sub- 

 stances in the extract upon the eggs, or yet again the rate of 

 oxidation may be decreased simply because the extract itself con- 

 tains substances which use up the oxygen in the water, and so 

 deprive the eggs of their otherwise available supply. No facts 

 can be brought forward at this time, however, to make any one, 

 or two, or all of these possibilities appear to be the probable ex- 

 planation of the phenomena under discussion. 



It should be emphasized at this point that the retardation caused 

 by the use of the extract results in arrests of development and the 

 production of abnormal types very similar to those caused by the 

 various chemical agents used, although it is not possible of course 

 to state definitely that these result from disturbances of the same 

 metabolic processes. 



