8 U. $. BUREAU OF FISHERIES. 
parent nuclei absent or in a weakened condition, with both in a 
weakened condition, or with the pronuclei incompatible through 
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 parthenogenesis, 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 accompanying cell division, multipolar mitoses, 
and delay in cleavage. The chromosome number in the eggs which 
seem to show normal development is haploid. 
Dungay (1913) weakened or injured sperms of several species of 
invertebrates by means of chemical treatment. heat, or staling, and 
development in eggs fertilized by such sperms resulted in delayed 
ee abnormally sized cells, multipolar figures, and similar 
efects. 
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 weakening 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. e 
It is not within the province of applied biology to go into a 
theoretical consideration of these phenomena. Suflice it to say that 
the weakening or injury of either sperms or unfertilized eggs will 
produce the same defects in the development of all animals so far 
investigated. Physiological and cytological 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 words, there is a weakening of either sperms or eggs before 
fertilization. 
It is highly improbable that natural conditions 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 fishes 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 
