STUDIES IN CYTOLOGY 401 
female is homogametic and the male digametic rather than with 
Strongylocentrotus (Baltzer, ’09),in which the female is digametic. 
I still feel that we are not yet able to apply one of the now 
accepted sex formulae to either Hipponoé or Toxopneustes. It 
is futile, at this time, to attempt to make a definite count of the 
chromosomes in these eggs. I feel reasonably sure that the num- 
ber in the zygotes is 37 and 38; but granting this to be true, no 
reliable conclusion can be drawn until we know the facts concern- 
ing synapsis in the formation of the germ cells. It is possible that 
the question can be settled only by the study of the odgenesis and 
spermatogenesis in these forms, but so much has been determined 
by the experimental method that one may hope that some Echino- 
derm may be found which will afford material favorable enough 
for deciding even this point. 
It is interesting in this connection to note that since the females 
of Hipponoé and Toxopneustes are homogametic we should 
obtain uniformly individuals of the same sex from chemically 
fertilized eggs. The conditions in Hipponoé indicate that these 
individuals would be female. 
It must also be noted that my results are not quite in accord 
with those of Miss Heffner. My observations would give us two 
classes of Toxopneustes zygotes, one with three and one with four 
V-shaped chromosomes rather than one with two and one with 
three. 
My investigation has shed no further light on the nature of 
these idiochromosomes; we do not know whether they are com- 
pound, whether they are single and have this individual form, or 
whether the form is due simply to the place of attachment of the 
spindle fiber. The last idea seems untenable in the light of their 
definite numerical occurrence. 
Turning from these purely cytological considerations to some 
of the facts concerning heredity in Echinoderms we must first 
notice that if one wishes to speak with accuracy it is now impos- 
sible to make the broad statement that all of the individuals of 
a given cross are maternal or paternal, or even intermediate, in 
a strict sense, in character. 
