NOTES ON SOME AQUATIC OLIGOCHATA, 213 
namely, a pair in Somite v1, and a long unpaired, asymme- 
trically placed sac extending through Segments vit, viii, Ix, 
and into x. 
Masses of developing ova were observed in Somites vii, 1x, 
XI, and a large ovum in Segment x. 
I have thought it worth while to figure the arrangement, as 
Dr. Bourne gives a different position for the “testes” and 
“ovaries” for Paranais littoralis, which I was unfor- 
tunately unable to find in a mature condition. He figures a 
large, asymmetrically placed mass occupying Segments viii 
and 1x, which he speaks of as “ testes,’ and he indicates as 
‘‘ ovary ”’ a single mass of developing ovain Segment x. Now, 
this would be a very exceptional position for the gonads in the 
family Naidide; and the “testis” of Oligochezta is not a 
large structure, but a small organ, occupying only a part of one 
segment. I cannot help thinking that Bourne has made a slip 
in writing of these structures as the gonads ; he meant probably 
to speak of them as the sperm-sacs and ovisacs respectively. 
It is a well-known fact that in the sexually mature Naid 
genital chetz replace the ventral bundles in Segment v1, and 
that the dorsal chetz, like the ventral ones, drop out, but are 
not replaced (fig. 40). 
I figure a portion of a nearly mature worm, 1.e. with 
sexual organs, in which the dorsal chetz are still in situ. 
The ventral chetz of one side are also present, but on the 
other side have been replaced by the genital chetz (fig. 41). 
These are stouter and longer than the ordinary ventral chete, 
and are not forked (fig. 38, c). 
The Supposed Constancy of m in a given Species 
of Naid. 
In a recent contribution (‘ Quart. Journ. Micr. Sci.,’ xxxii, 
Part 2, June) on the Naidide, Professor A. G. Bourne adds 
many facts to our knowledge of the family, and gives the 
position of the zone of budding for many of the species, but 
says nothing about it for N. elinguis. He regards the 
position of the zone of budding as a constant character for 
