810 EEPORT OF COMMISSIONER OF FISH AND FISHERIES. [16] 



tion. Inasmuch as we have lowered the temperature of the air and 

 water, the media in which the ova of the shad underwent their devel- 

 opment, and fiud that it is retarded in consequence, we must naturally 

 conclude that the rate of segmentation, upon which the rate of develop- 

 ment directly depends, has been in some way interfered with or impeded 

 in its progress. Since we also saw that the rhythmical metamorphoses 

 of the nuclei were directly concerned in the process of segmentation — 

 that in them the vis essentialiSy essential force of segmentation, really 

 resides — it appears to me that we are also really bound to conclude 

 that the fall in the temperature has affected the activity of this vis essen- 

 iialis of the nuclei, which are retarded in their metamorphoses, in con- 

 sequence of which the rate of segmentation and development is retarded. 

 This fully and clearly accounts for the resulting prolongation of the 

 normal period of development when the temperature of the media in 

 which the ova undergo their evolution is lowered as much as is consist- 

 ent with their regular, healthful incubation. 



If retardation is possible it ought also to be possible to accelerate de- 

 velopment. For centuries it has been the practice to accelerate and 

 maintain the growth of plants in hot-houses and forcing-pits during in- 

 clement seasons of the year. This is proof enough, as far as the vegeta- 

 ble kingdom is concerned, that acceleration of the processes of growth, 

 which simply means that the acceleration of fissiiDarous cellular prolifer- 

 ation or segmentation is here possible. Its philosophy is the same in 

 principle as that of retardation ; acceleration is the converse or recipro- 

 cal principle as opposed to the former. According to a table given by 

 Mr. E. E. Earll, in his paper on the development of the cod, in the 

 United States Fish Commissioner's report for 1878, page 724, we learn 

 that the minimum time of incubation for the ova of this fish is thirteen 

 days, temperature of sea- water 10° F. ; the maximum time, according to 

 the same authority, is fifty days, temperature of sea- water 31° F. Our 

 own experience at Wood's Holl last winter taught us that the develop- 

 ment of the ova of the cod was capable of being accelerated, for those 

 in a glass cone near a warm stove hatched out in a shorter space of 

 time ;^ sixteen days) than any others. Our power to accelerate the rate of 

 development of the cod may be of use, as we may thereby be enabled to 

 hatch out a large percentage of ova in a very few days. Whether the 

 young would be as vigorous as those incubated in the natural way re- 

 mains to be learned. 



Acceleration, like retardation of development, is accomplished by in- 

 fluencing the rate of the rhythmical metamorphoses of the nuclei of the 

 cells of the embryo. Accelerate the rate of these metamorphoses and 

 segmentation is hastened so us to cause development to proceed more 

 rapidly. The stimulus is heat, a mode of motion, and we are forced to 

 believe from what has preceded that the nuclear metamorphoses are 

 simply the specific modes of motion of the cellular life centers. The 

 molecules of the nuclear spindles, reticuli, &c., are made to move more 



