VARIATION IN ECHINOID PLUTEI 
673 
Since neither the defects nor the multiplicities appear as such 
in the tables of constants, although the defects have influenced the 
size of the mean in every case, a separate treatment of these varia- 
tions is necessary. I mention these as percentages in the various 
series studied. 
Series I. 
2 days. No anal arms (type, fig. 9), 1 per cent. 
No left oral arm, 1 per cent. 
3 days. No anal arms. 8 per cent. 
No oral arms, 7 per cent. 
4 days. No anal arms, 16 per cent. 
No oral arms, 28 per cent. 
5 days. No defects. 
Series II. 
2 days. No anal arms, 1 per cent. 
No oral arms, 6 per cent. 
No left anal arm (type, fig. 10) 2 per cent. 
With both multiple right and left anal arm (type, 
fig. 12), 3 per cent. 
With multiple right anal arm (t3^pe, fig. 11), 4 
per cent. 
With multiple left anal arm, 5 per cent (one with 
three rods). 
3 days. No anal arms, 3 per cent. 
No oral arms, 4 per cent. 
^Multiple right anal arm, 2 per cent. 
Multiple left anal arm, 2 per cent. 
Left anal arm cleft (type, fig. 17), 1 per cent. 
Slightly cleft pre-oral region, 5 per cent. 
4 days. No oral arms, 4 per cent. 
Multiple left anal arm, 2 per cent. 
Slightly cleft pre-oral region, 4 per cent. 
5 days. No left anal arm, 1 per cent. 
No left oral arm, 1 per cent. 
Multiple right anal arm, 1 per cent. 
Multiple left anal arm, 2 per cent. 
Slightly cleft pre-oral region, 2 per cent. 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 9, NO. 4. 
