282' 
W. M. Wheeler 
cells of the other species, is reduced to a mimber of vacuoles be- 
tween which runs a coarse net-work. Beyond this I was unable 
to make out any structure in these rudimental organs. 
What is the function of these segmental sacs? From their 
ectoderma! origin they may be glandulär, sensory or respiratory in 
function. Their structure is obviously ill-adapted to respiration, so 
that this possibility may be excluded. It is much more difficult to 
decide between the two remaining functions. 
When I first saw these organs, I was inclined to accept Nansen's 
view that they are excretory or secretory in function. Not having 
seen the nephridia at that time, I proceeded to test the validity of 
the Norwegian zoologist's view by placing a number of specimens 
of M. glahrum for 24 hours in sea-water containing powdered car- 
mino. By the end of that time the sacs stood out as four deep red 
Spots along either side of the body, and I at once concluded that 
the Carmine had been taken up through the intestine and deposited 
in the walls and cavities of the sacks. A single series of sections, 
however, soon proved to me that I was entirely mistaken; there was 
a small amount of carmino in the intestine and its branches, but 
none whatever in the cytoplasm of the largo succulent cells forming 
the walls of the sacks. The cavities of the sacks and the Spaces be- 
tween the folds of their walls were full of carmino, but it had been 
drawn in from the outside, probably by a movement of the cilia 
surrounding the sacs and by the Inversion of the sacs themselves. This 
experiment was repeated several times. In many cases the animals 
would not swallow the carmino, but their suckers would take it up 
nevertheless. These experiments, besides showing that the sacs are 
probably not nephric organs, will explain the presence of the mucous 
granulös of Nansen in the cavity. These are very probably only 
secretions of the true nephridia or feces which have been taken in 
from the outside. If a M, glahrum be placed on its back and the 
orifices of its segmental sacs carefully examined with a lens, one 
will often see a few granulös of matter thrown out of a sac, especi- 
ally when it is about to be everted. These granulös I take to be 
the same as those figured by Nansen. 
The second alternative, viz. that the segmental sacs may be 
sense-organs, seems to me to be more plausible. I take them to be 
in all probability the homologues of the lateral line organs 
(Seitenorgane) which have been described in many Chaetopods 
(Capitellidae, Eisig '79,'87; Polyophthalmidae, E. Meyer '82; Amphi- 
