8 U. S. BUREAU OF FISHERIES. 



j)arent nuclei absent or in a weakened condition, with both in a 

 weakened condition, or with the pronuclei incompatible throu<2:h 

 hybridization. A limited survey of the extensive literature on this 

 subject will suffice to show the trend of the work. 



E. B. Wilson (1901) found that in artificial partheno^renesis, where, 

 of course, only one of the parent nuclei is present, there occur such 

 abnormalities as the formation of cytasters, the multiplication of 

 chromosomes without accompanyinf^ cell division, multipolar mitoses, 

 and delay in cleavage. The chromosome number in the eggs which 

 seem to show normal development is haploid. 



Dunga}^ (1913) weakened or injured sperms of several species of 

 inA-ertebrates by means of chemical treatment, heat, or staling, and 

 development in eggs fertilized by such sperms resulted in delayed 

 cleavage, abnormally sized cells, multipolar figures, and similar 

 defects. 



O. Hertwig (1911) and G. Hertwig (1912). among others, have 

 described the effect of fertilizing eggs with sperms treated with 

 radium. Both authors remarked especially a budding phenomenon 

 correlated with delayed development. They also describe drawn-out 

 nuclei, multiplication of chromosomes in a nucleus, giant nuclei, and 

 cytasters, all almost identical with phenomena which we have de- 

 scribed in the abnormal pike-perch eggs. 



C. Packard (1914) found that sperms which had been treated with 

 radium may stimulate the eggs to cleave but fail to take part them- 

 selves in the subsequent development. When the eggs are " radi- 

 ated," they show various irregularities, such as abnormal divisions 

 or the failure of pronuclei to unite. 



G. and P. Hertwig (1914) produced similar effects to those already 

 mentioned by Aveakening sperms with methlyn blue among other 

 reagents. Still more striking are the phenomena produced by fer- 

 tilizing the eggs of teleosts with sperms of another species of teleost. 

 The whole list of abnormalities given above was reproduced in such 

 development. 



It is not within the province of applied biology to go into a 

 theoretical consideration of these phenomena. Suffice it to say that 

 the weakening or injuiy of either sperms or unfertilized eggs will 

 produce the same defects in the development of all animals so far 

 investigated. Physiological and cj^tological phenomena identical in 

 appearance with those produced experimentally in this way have been 

 observed also in abnormally developing pike-perch eggs, and it sug- 

 gests itself that the cause of such irregularities is of similar nature. 

 In other Avords. there is a weakening of either sperms or eggs before 

 fertilization. 



It is highly improbable that natural condition^; should induce a 

 state that would cause such a large mortality in the embryos, and it 

 becomes almost certain that the injury is incurred during the period 

 of the captivity of the fishes. 



As has been said in the introduction, most of the iishes are found 

 not to be ready for stripping when first caught. They are therefore 

 retained in pens or crates until the reproductive products can be 

 obtained from them by stripping; in other words, until they are 

 "ripe." The penning of fishes prior to spawning is a practice of 



