58 
Psyche 
[March 
612 had the normal 37. In 63 cells of a female from Florida 
(normally 53 chromosomes), 40 were normal and 23 cells had 106 
chromosomes. These 2 individuals which had some cells with double 
their normal number of chromosomes may possibly have resulted 
from the colcemid treatment. 
None of our clones of P. surinamensis had modal numbers of 36 
or 38 as reported by Suomalainen (1945) and Matthey (1945, 
1948). These writers did not indicate the number of cells counted, 
so it is unknown if the numbers given by them are the usual numbers 
present. Considering the variation in the clones we examined, it is 
quite possible that the numbers they give predominated in the in- 
dividuals of their colonies. 
The types of chromosomes found in Pycnoscelus (Figs. 18-26) 
from different localities are summarized in Table 4. There are 3 
classes of chromosomes: median, submedian, and subterminal. Me- 
dian chromosomes predominate and usually there appear to be only 
1 or 2 subterminals. The males of P. indicus have one less sub- 
terminal chromosome than their respective females. This is also 
true of the Thailand parthenogenetic male and suggests that the 
subterminal chromosomes may be the X chromosomes. However, 
arguing against this is the fact that the Bogor female appears to lack 
subterminals and the parthenogenetic females from Florida and Belem 
(53 chromosomes) lack one subterminal (Table 4), which should 
have made them males, if the subterminals were sex chromosomes 
and if these females have only 2 X chromosomes. In addition, if the 
Panama and Jamaica clones are triploids, the females should have 
3 X chromosomes, and they apparently have only 2 subterminals 
(Table 4). It should be pointed out that several sources of error 
may affect the categorizing of some of the chromosomes. Not only 
may colcemid treatment affect the relative lengths of the arms be- 
cause of contraction (Sasaki, 1961), but some of the chromosomes 
are so small that errors could be made in determining the location 
of the centromeres, and also in measuring the lengths of the arms. 
Most of the median chromosomes are readily classified, but there are 
some chromosomes which are on the borderline of the 3 categories. 
In P. indicus some individuals have 2 less chromosomes than others. 
There is no way of telling whether the parthenogenetic forms arose 
from bisexual stocks with 2n = 36 or 38 chromosomes (Table 5). 
For example, the Brazilian and Australian forms (34 chromosomes) 
may have lost 2 submedians if they came from a 211 = 36 $ or, they 
may have lost 2 medians and 2 submedians if they came from a 
