BULLETIN OF THE UNITED STATES FISH COMMISSION. 179 



hours; the dififorence in the temperature of the water used is only 

 IG.8'^ F. Is there a limit to the possibilities of retardation? Experi- 

 ment has shown that there is. The temperature of ice- water, 38° F., 

 was found to be fatal at the morula or germinal disk stage of develop- 

 ment of the shad egg, in the course of experiments made at Havre de 

 Grace, Md., in 1880. The cells of the germinal disk became brownish, the 

 cleavage furrows obliterated, the disk tended to spread out and become 

 larger across. These phenomena indicated stagnation of development 

 and death. The second series of experiments, conducted by what is 

 known as the "dry method" in a refrigerator box provided with canton- 

 flannel trays, devised by Mr. F. K. Clark especially for these experi- 

 ments, gave better results. We found that the ova merely kept damj) 

 on the trays in an air temperature of 52° appeared to develop quite 

 normall}^, the only serious drawback being the rapid and more or less 

 fatal development of fungus, the mycelium of which would soon grow 

 over the eggs, iienetrate the membranes, cause them to collapse, trans- 

 form the protoplasm of the vitellus into fungus protoplasm and kill 

 the ova. 



The following abstract from my note-book, recording what was ob- 

 served in watching the results obtained from a trial of Mr. Clark's 

 apparatus, speaks for itself, though it would facilitate the comprehen- 

 sion of the matter if a series of explanatory figures could be introduced: 



" Eggs taken June 8 and put into refrigerator at 9 o'clock p. m. ; exam- 

 ined June 9 at 9 o'clock a. m. ; exposed for 12 hours to a temperature 

 ranging from 54° to G0° F. Cleavage has advanced to the morula stage ; , 

 i. e., the germinal portion of the egg is still discoidal, lies on one side 

 of the vitellus or yelk, and has not advanced beyond the condition ordi- 

 narily reached in three hours with the temperature 72° F. 



" Same lot, June 9, 2.30 p. m., not advanced but a little beyond the 

 stage just described above; the germinal disk still maintains its char- 

 acteristics ; development normal ; temperature 51° F. 



"Same lot, June 10, examined at 9.30 a. m. ; segmentation cavity de- 

 veloped and blastoderm forming ; incipient embryo making its appear- 

 ance at one side. The blastoderm, however, does not yet cover more 

 than half of the upper hemisphere of the vitellus, a condition ordinarily 

 attained in six hours with the temperature of the water at 72° F, 

 Temperature in refrigerator box now ranging from 52° to 51° F. Eggs 

 of the same age, 30^ hours in a hatching-jar, have the vitellus com- 

 pletely inclosed by the blastoderm, the embryo formed, with eyes, ears, 

 and brain distinguishable, and the tail is budding out as a small, 

 rounded knob at the posterior end of the embryonic axis, which curves 

 around one side and now extends from one pole of the egg to the other, 

 embracing an arc of 180°. 



" Same lot, in refrigerator, examined June 10, at 8.30 p. m., or nearly 

 forty-eight hours after impregnation, show that tbe blastoderm has 

 grown down half way over the vitellus, like a hemispherical caj) ; the 



