188 



Scientific Proceedings (114). 



or out of the blood stream. The response to a hot environment is 

 peripheral vasodilation plus hemodilution ; a cold environment 

 evokes vasoconstriction plus hemoconcentration. 



To simplify the above presentation the rectal temperature 

 readings have been omitted ; these showed in the case of the cold 

 baths and sometimes in the case of the hot, that the bath condi- 

 tions were too extreme for the animal to withstand in spite of the 

 regulatory responses. 



Confirmatory evidence has been accumulated since the above 

 experiments were carried out. 



93 (i675) 



The life history of an amicronucleate race of Didinium nasutum. 



By MARY W. PATTEN. 



[From the 0 shorn Zoological Laboratory, Yale University \ 



A series of pedigree lines of Didinium nasutum, consisting of the 

 progeny of a single exconjugant, were bred continuously under 

 practically constant environmental conditions from December 16, 

 1919, to September 10, 1920. 



A cytological investigation of the preparations made daily 

 from stock left after each isolation, demonstrated the absence of a 

 morphological micronucleus in vegetative, dividing and conjugat- 

 ing animals. In the race from which these pedigree lines were 

 derived by conjugation, and also in other unrelated races of 

 Didinium, micronuclei were easily demonstrable. It is clear, there- 

 fore, that the parent race was micronucleate, while one of its 

 progeny, a single exconjugant (the original cell of the race under 

 investigation) was amicronucleate. Moreover, this amicronucleate 

 condition persisted throughout the life of the race, that is, through 

 652 generations. 



At various intervals during the life history of this culture, 

 periods showing a tendency for encystment and conjugation 

 occurred, but the animals which encysted or conjugated invariably 

 died, a fact undoubtedly related to their amicronucleate condition. 

 Rhythmical periods of depression followed by increased vitality, 



