LOW TEMPERATURE DEVELOPMENT OF FUNDULUS 457 



like; heart undifferentiated into chambers; only the sinus end of 

 heart contractile; well-marked rhythms in rate of contraction of 

 heart, sometimes occasionally stopping; no circulation, either 

 on account of absence, or proximal or distal closure of the heart 

 few vessels over the yolk; yolk- vessels abnormally arranged 

 heart thread-like but with a good and complete circulation 

 very few erythrocytes but abundant plasma circulating freely 

 erythrocytes in masses on postero-dorsal surface of yolk; large 

 masses of erythrocytes antero-ventral to heart or along the an- 

 terior margin of pericardial cavity (after hatching this latter 

 mass was in a median ventral position) ; dense mass of erythro- 

 cytes collected in tail, i.e., caudal aorta and vein anastomosing 

 at base of tail. 



Many more abnormalities might be mentioned and of course 

 innumerable minor details of abnormal character might be cited 

 from the material. What variety of conditions might be re- 

 vealed by the thorough study of sections of these embryos can 

 only be imagined. 



One further point might be mentioned. Stockard observes 

 ('15, p. 26) that embryos developing without a circulation are not 

 able actually to hatch. As a rule I had a similar experience but 

 one exception was so remarkable that it seems worth noting. 

 After eleven days at 10-1 1°C., one lot of eggs which had devel- 

 oped in the laboratory for twenty-three hours before cooling, 

 showed many normal embryos, for the most part at a stage 

 when the optic vesicles were just forming. Others were grossly 

 abnormal or entirely dead. Among those appearing normal 

 upon removal from the cold, manj^ abnormalities appeared later 

 and one of these, which was found hatched twelve days after 

 removal, or twenty-four after fertilization, had no circulation 

 whatever, although the heart was present and pulsating weakly. 

 This, however, was not its only defect. It was below average 

 size, had but a single median anterior eye and correspondingly 

 the nose and upper jaw region were, as usual in cases of cyclopia, 

 narrow and elongated, the tail was short and ended in an un- 

 differentiated mass, pigment cells were largely massed on the 

 ventral surface of the yolk. It seemed unable to direct its swim- 



THE AMERICAN JOUKNAL OF ANATOMY, VOI.. 20, NO. 3 



