XVI -ON THE RETARDATION OF THE DEVELOPMENT OF THE 

 OVA OF THE SHAD (ALOSA SAPIDISSIMA), WITH OBSERVA- 

 TIONS ON THE EGG FUNGUS AND BACTERIA.* 



By Jonx A. Ryder. 



Several series of experiments at different times were undertaken by 

 persons connected with the United States Fish Cemmissiou having for 

 their object the solution of the following problems : " Is it i)Ossible to 

 lower the temperature of the water in which shad-eggs are incubated 

 so as to greatly retard and prolong the process ? " " Is it possible to 

 prolong the period of incubation so that large quantities of embryo- 

 nized ova may be carried for long distances by land or water, so as to 

 effectively stock distant or foreign waters ? " These two queries, I think, 

 clearly state the objects of the experiments, and also tacitly indicate 

 the important results which would follow in case practical results should 

 be attained. 



That a decrease in temperature would impede or retard the develop- 

 ment of ova has been known for a long time, and, without encumbering 

 this essay with references it may be asserted as a truth based on phys- 

 ical reasons and facts. Physiologists and biological philosophers, such 

 as H. Milne-Edwards and Herbert Spencer, have recognized and dis- 

 cussed the influence of fluctuations of temperature on physiological 

 processes. Every genus and perhaps even every species of fishes, in 

 the course of the early development of its ova, appears to present some 

 idiosyncrasy of behavior which demands that its characteristics shall 

 be studied before it is ventured to i>roceed with exijerimeuts of this 

 character. Practically the peculiarities of the ovum of the shad are 

 perhaps as well known as those of any species we are called upon to 

 deal with. 



Shad-eggs after impregnation are relatively large, measuring from 

 one-eighth to one-seventh of an inch iu diameter. When first extruded 

 from the parent fish they measure about one-fourteenth of an inch in 

 diameter, are somewhat flattened and irregularly rounded in form ; 

 the egg-membrane, a true so7ia radiata^ is much wrinkled and lies in 

 close contact with the contained vitellus. Immediately after impreg- 

 nation this membrane becomes tense, is filled with water which has 

 found its way through the membrane from the outside, and is now x^er- 



* Second edition, revised. 

 [ 1] 795 



