152 CHARLES R. STOCKARD 



only lack of perfection in this control of more than 50 individuals. In 

 Bi there was one unhatched monster. In Bo 10 were still unhatched, 

 though 6 seemed normal and ready to hatch; therefore, the cold treat- 

 ment greatl}' reduces the strength and delays the hatching moment 

 of these embryos. In B3 3 were unhatched. In Ci 8 were unhatched, 

 7 of these were deformed, one being a twin specimen and one almost 

 normal. 



This series of experiments further shows the possibility of 

 almost stopping, or reducing to an extreme degree, the rate of 

 development during the earliest cleavage stages and again resum- 

 ing a more or less normal rate on the part of a few individuals. 

 An almost complete stoppage at an early cleavage stage results 

 in a very high mortality ranging from as great as 78 per cent and 

 54 per cent, down to 34 per cent. However, the reduction in 

 rate brought about by a less severe temperature of 9°C. does not 

 cause so great a mortality and does not prevent the resumption of 

 development of almost normal rapidity. 



It is clearly show^n, how^ever, that although certain specimens 

 may resume a fairly normal developmental rate after such treat- 

 ments, the early arrests have had injurious effects upon the 

 quality of the resulting embryos. A considerable percentage of 

 gross abnormalities occurs in all of the groups, and even those 

 embryos which appear on close examination to be normal in 

 structure are extremely slow in hatching and are not in all cases 

 capable of typical swimming reactions and perfect behavior as 

 young fish. 



A point of particular importance is that in such a series as this 

 w^hich had been arrested during an early cleavage stage, the 

 monsters resulting are not limited to any particular type, but 

 exhibit, in a series of sufficient extent, almost all known types. 

 There may occur double monsters of varying degrees, from sepa- 

 rate twins, fused but with complete bodies and tails, to double 

 bodies and single tails, and finally different degrees of double- 

 headedness on single bodies. There are specimens exhibiting 

 anophthalmia, monophthalmia, microphthalmia, cyclopia, and 

 all types of malformed eyes. The brains may be slightly asym- 

 metrical, irregular, tubular wdth no primary ventricles, or de- 

 formed in various ways. The mouth and branchial region may 



