Abnormal Developmejit of Toad Ova 1 7 



experiment ova were divided into two lots, one of which was kept 

 in lake water and one in the harder city water. 



May 6. Between 50 and 75 per cent of the eggs in each of the 

 four lots were in the blastula stage. 



May 7. All fertilized eggs were in the gastrula stage. 



May 8. All fertilized eggs were advanced to the stage in which 

 the yolk plug appears smiJl. 



May 9-22. The eggs in the city water during this period devel- 

 oped much more slowly than the lake water eggs. The control eggs 

 in the city water were apparently nearly all fertilized and developed 

 apparently normally though slowly up to May 12 when, owing 

 to the cover being left off the shallow dish in which they were con- 

 tained, and consequent evaporation of water during the absence of 

 the writer from the city, the whole lot was destroyed. Of the 

 experiment ova kept in city water about 50 per cent developed. 

 On May 11 seventeen unfertilized and partially developed eggs 

 were removed, leaving eleven nearly normal larvae with very short 

 caudal processes. On May 13 only six of these were still alive. 

 These six were then transferred to lake water. Two could move 

 about by movements of the body and tail. The other four showed 

 little power of motion. These four larvae and one of the two more 

 motile ones did not grow much more in size but became quite 

 abnormal in external form similar to those pictured in Plates II to 

 V. One of the two more motile larvae developed into a tapdole 

 fairly normal in external form, although it died before any of the 

 controls which were kept in the lake water. 



Of the control ova in the lake water four eggs were unfertilized 

 and nine developed into perfectly normal tapdoles which were 

 kept alive for several weeks. Of the experiment ova on May 1 1 

 eight unfertilized or undeveloped eggs were removed, leaving 

 seventeen larvae with slightly developed heads and very short 

 caudal processes. On May 13 the control larvae could swim for 

 short distances. None of the experiment larvae could do so. 

 Externally the latter had begun to exhibit various abnormalities 

 which became more marked from this period on. About a dozen 

 of these larvae w^ere preserved on May 14. The others all died 

 a few days later, /. ^., in from ten to fourteen days after the 



