678 
DAVID H. TENNENT 
of changes in the environment during development/' while I 
have tried to determine the amount of variation and the direc- 
tion of variation in distinct lines kept, so far as possible, in uniform 
environments. 
Vernon's results and my own are in some respects complemen- 
tary and I hope, at no distant date, to make a detailed compari- 
son of his numerical results with mine. 
Steinbriick's work deals particularly with the variations that 
I have termed multiplicities. It is interesting to see that Strongy- 
locentrotus, with which these investigators, Vernon and Stein- 
briick, have worked shows some of the multiplicities that are shown 
by its relative, Toxopneustes, which has been the species under 
my observation. 
In section 1 of this paper the differences in variability and the 
amount of variation from day to day have been shown. The only 
comment that I wish to make is that in the various series, as will 
be seen by an inspection of the graphic representations, there is 
not a symmetrical grouping about the mean. A closer approach 
to symmetry is seen in the combined Series I-V and an approxi- 
mation to the theoretical curve is made by the individuals that 
I have checked in Series III as ^^normal.'' 
My observations on the individual series agree with Vernon's 
anal arm measurements (a measurement of the anal arm length 
and not including the body length). 
In Section 1 it has further been shown that there are character- 
istic type or line variations. These are : 
Series I. Defects in arms. Long oral arms. 
Series II. Multiple right and left anal arms. Slightly cleft 
pre-oral region. 
Series III. Slightly cleft pre-oral region. 
Series IV. Weakness. 
Series V. Defects in arms. 
Series VI. Multiple rods. 
Series VII. No marked characteristics. 
* Series VIII. Extreme variation as to multiplicities and defects. 
Series IX. Single median anal arm containing two or more bars. 
