294 WILBUE WILLIS SWINGLE 
entirely independent. By means of these vesicles the chromo- 
somes preserve their identity through the so-called resting stages. 
8. The cells and chromosomes of the larvae are considerably 
larger than those of the adult frog, and more nearly resemble the 
cells and chromosomes of urodeles than those of the adult of their 
own species. 
9. This size difference between the larval and adult cells and 
chromosomes is explained in detail in the text and is considered 
to be due in part to the number of intervening cell divisions, 
with reduction of cell and chromosome size the greater the num- 
ber of divisions, and to reduction in cell size at the time of 
metamorphosis due to loss of water from the tissues. 
10. The haploid number of chromosomes in the larvae is four- 
teen. The tetrads of the first larval sexual cycle are extremely 
large and of the open-ring type characteristic of urodeles. They 
differ markedly from the type of tetrad appearing in the second 
larval sexual cycle. 
11. Conjugation of the chromosomes is by parasynapsis, and 
occurs in the amphitene stage, when the leptotene threads twist 
together to form the pachytene. 
12. Evidence of 'crossing-over' during diakinesis, such as fig- 
ured by Janssens for Batracoseps, has not been observed, or 
rather, has been observed but not interpreted as such. The 
chiasma-type which appears during diakinesis stages of the bull- 
frog larvae has been interpreted by the writer as tetrads opening 
out in two planes at right angles to one another thus giving the 
appearance of 'crossing-over' of the chromatids. 
13. It is suggested that 'crossing-over' occurs during the amphi- 
tene stage, when the conjugating leptotene threads coil tightly 
about each other corkscrew fashion. 
14. The first larval maturation cycle is normal in every respect 
save for the size of the cells and chromosomes, up to the formation 
of the first maturation spindle. The spermatocytes degenerate in 
the act of division. 
15. The cause of the degeneration of the larval spermatocytes 
is the abnormal behavior of the centrosome which fragments, 
forming accessory asters and spindles. It is recognized that the 
