214 W. BLAXLAND BENHAM. 
the various species, and designates this position by », which 
signifies the number of segments in front of the zone. 
Now, from my recent observations on this phenomenon, 
some of which were made before the publication of Professor 
Bourne’s paper,! I believe that he is rather too dogmatic on 
this point ; for he only mentions one exception, and that for 
Pristina breviseta, A. G. B., whereas I have found 
considerable divergences in the value of ” from the value 
given by him. For example, a number of Stylaria lacustris, 
collected in different places and at different times, were examined 
from this point of view. 
Dr. Bourne gives for this species “‘n = 27.” I find, how- 
ever, as will be seen from the following table, a good deal of 
variation in the position of the zone. The list refers to two 
sets of specimens, each individual being indicated by a letter. 
A io One 4 : ‘ n = 30 
B re fl Cas ; : n= 24 
C 7 24 eles : : m= 4 
D pi) Uae Oe es ‘ : t= 2) 
HK m = 24 
Six specimens were without zones. 
In another lot— 
K p : 2 12 (ane f , nm == 25 
L , ‘ F ion Oo eee < 5 nm = 34 
INE ae oe ‘ A nm = 30 
Three specimens showed no zone. 
In all these cases I am counting as Professor Bourne counts; 
namely, the 1st setigerous segment is Segment 11, so that the 
first dorsal bundle occurs in Segment v1. 
Again, in Nais barbata he states, on p. 344, “n= 17.” 
I examined a limited number of these, and found the number 
by no means restricted to 17. I have unfortunately mislaid 
my notes on the point, but four specimens, taken at random 
before I had seen his paper, were stained and mounted. 
Of these two have n = 14, and in the two others z = 15, 
1 Professor Lankester kindly allowed me to see a proof of the paper, and 
my attention was thereby drawn more particularly to some of these points. 
