12 MARGAEET MORRIS 



suits from these experiments, of which there are twenty- two. 

 Eight gave no larvae at all, twelve gave few, or very few, and 

 only two gave over 0.2 per cent. The highest percentage ob- 

 tained was 4 per cent. These experiments are set forth in 

 detail in table 2. 



Finally, a few experiments were made with a temperature of 

 35-37°C. If the eggs are subjected to this temperature for ten 

 minutes, fragmentation ensues. The optimum length of ex- 

 posure is two minutes, but there was only one of the eleven 

 experiments with this temperature which resulted in the forma- 

 tion of larvae, and in this case they were very few. Table 3 

 shows the results of these experiments. A few experiments 

 were made with temperatures below 32°C. but they were entirely 

 unsuccessful. 



b. Experiments to show that larvae come from eggs which have 

 not formed polar bodies. Up to this point, no mention has been 

 made of the effect that different exposures to heat have on polar 

 body formation. We must consider this question, as it gives 

 the first evidence that it is eggs which have not formed polar 

 bodies that develop to larvae. It has been seen that exposing 

 the eggs to 32-33°C. for an hour gives the highest percentage of 

 larvae, while the two-minute exposure to 36-37°C. gives very 

 few larvae, or none at all. It is, however, the latter group of 

 experiments which gives the highest percentage of polar body 

 formation. Compare, for instance, No. 53 (table 3) and No. 

 65 B (table 1). In the first, polar bodies were formed in almost 

 all the eggs, but only 2 per cent divided, and none developed to 

 larvae. In the second, the polar bodies were very few, while 26 

 per cent of the eggs divided and 18 per cent grew to larvae. 

 These experiments represent the extremes, and perhaps the 

 point is more fairly illustrated by an experiment in which one 

 lot of eggs was divided into two portions. One half was ex- 

 posed to a temperature of 36-37°C. for two minutes, the others 

 kept at 32-33°C. for thirty minutes. The first half showed 22 

 per cent with polar bodies, hardly any cleavage, and no larvae; 

 the second had 10 per cent polar body formation, 25 per cent 

 dividing and 0.2 per cent larvae. 



