476 The Origin of Polyploids 



of stearic acid, morpholine, or lanolin. Other methods have also 

 been used. 



Animals 



Polyploidy is far less common in animals than in plants, but 

 some attempts have been made to induce polyploidy by the use 

 of colchicine. As in plants, the formation of the spindle appears 

 to be inhibited and dividing cells remain in metaphase. In most 

 animals, the treated cells do not proceed from c-metaphase mto 

 the following resting stage with a doubling of the number of 

 chromosomes, but degenerate, thus ending any possibility of 

 polyploidy. In a few experiments, cells with the double number 

 of chromosomes have been produced as the result of colchicine 

 treatment, but they have not lived long or produced polyploid 

 organisms. When colchicine was applied to eggs of Arbacia 

 punctata ten minutes after insemination, the cell remained in 

 metaphase when the concentration of the colchicine was above 

 10"^ molar, but somewhat lower concentrations allowed the 

 nucleus to divide abnormally although cleavage was impeded. 

 At concentrations as low as 10~^ molar the rhythm of division 

 during the early cleavage stages is not affected, but the subse- 

 quent development of the larvae is markedly stunted. Nebel 

 summarizes the effects of colchicine in increasing concentrations 

 as follows: normal cleavage is affected; astral rays fail to form; 

 the spindle is reduced in size; the spindle fails to form; the chro- 

 mosomes become pycnotic and fail to divide normally. 



In higher animals several interesting experiments have been 

 carried out. Pincus and Waddington subjected the fertilized 

 rabbit egg developing in culture to dilute solutions of alcohol, 

 ether, or colchicine in different strengths and for different lengths 

 of time, or to brief exposure to temperatures above the normal. 

 Good mitotic figures were observed for 40 eggs, and 15 of these 

 were tetraploids. Of these, 13 were from eggs treated with col- 

 chicine and 2 from eggs treated with ether or alcohol. Colchicine 

 prevents spindle formation and appears to inhibit cleavage by 

 inhibiting almost all cytoplasmic movements and slowing down 

 nuclear activities. The tetraploid ova ordinarily failed to cleave 

 during 24 hours, but a few did undergo cleavage at a subnormal 

 rate. Treatment with colchicine solutions of 24-hour chick em- 

 bryos have been reported in a preliminary note by Higbee. She 



