BULLETIN OF THE UNITED STATES FISH COMMISSION. 187 



could not go on to any hurtful extent. The low temperature would also 

 tend to arrest any tendency to putrescence. 



How to maintain a uniform temperature in the refrigerators, so as to 

 guard against dangerous fluctuations of temperature, appears to me to 

 be a matter of some difficulty, because sudden meteorological changes, 

 such as we sometimes experience in this latitude, would influence the 

 working of the apparatus. The best regulator would probably be a 

 faithful attendant. The control of the temperature of the water flowing 

 through coils surrounded with ice, is, in the light of experience, a com- 

 paratively easy matter, as it has been found that in a coil of a given 

 length the fluctuation in the temperature will not vary more than three 

 or four degrees, if a little attention is bestowed in regulating the flow 

 and keeping a good supply of ice packed around the coils. 



The prevention of leakage or loss of water from the apparatus would 

 be entirely overcome, both on board cars and steamships, by the adoption 

 of the closed glass hatching-jars, of various forms, devised by Colonel 

 McDonald. They ai)pear to be cheaj), and are very economical of room. 

 There can therefore be no objection to the introduction of the api)aratus 

 into vessels and railway express cars on the score that it makes objec- 

 tionable slop and slush on the floors or decks. 



The foregoing, it appears to me, is an approximate solution of the 

 problems which we set out to answer; whether we are right another 

 season's work ought to enable us to decide practically and finally, as we 

 can now take up the subject intelligently ; the preliminary experimental 

 work has been completed. 



appendix on the histological rationale of re- 



tardation! 



Every developing ovum is made up of certain cellular elements, each 

 one of which is i)rovided with a central nuclear body, which apijears in 

 the light of recent researches to be the directive dynamic center of all 

 further changes involved in the successive cleavages undergone by the 

 cellular elements constituting that portion of the egg immediately con- 

 cerned in the formation of the embryo. The assumed disappearance of 

 the nucleus of the egg has been proved not to take place in the act of 

 impregnation, in not only invertebrate ova, but also in vertebrate ones as 

 well. The hypothetical assumption of a cytode or moneron stage of de- 

 velopment in the ova of all forms by Haeckel does not, therefore, appear 

 to be sustained by facts. These and other known facts, such as the recent 

 observation of the metamorphoses of the nuclei of Rhizopodsin the act 

 of division (multiplication), also throws doubt on the existence of the 

 Monera themselves, as Von Hensen has suggested. Nuclear networks 

 inside of cells, as well as intranuclear networks, seem to be of almost 

 universal occurrence according to the. researches of Flemming, Klein, 

 the Hertwigs, Pfltzner, Fol, and others on animals and man, and by 



