CONTRIBUTIONS TO THE ANATOMY OF EARTHWORMS. 427 
known and in but few types. It seems possible, however, that 
the median unpaired sperm-sacs in this and in other Earth- 
worms may represent the sperm-sacs, which are also median 
and unpaired, of many aquatic forms, while the paired sperm- 
sacs which are in A. georgianus quite independent of the 
median sac may be structures unrepresented in those forms. 
The extent of the median sac in A. georgianus through a 
number of segments is quite comparable to what is found, for 
example, in Clitellio. 
The penial setz are illustrated in figs. 15, 16. A remarkable 
fact about them is that there are two kinds; in one kind the 
extremity is ornamented with scallop-shell-like processes ; in 
the other kind the extremity is plain; this is not a difference 
due to age. So far as I was able to ascertain, the ornamented 
sete form one bundle, the plain setz another. 
Septal Sacs (figs. 31, 32).—A very characteristic feature, 
which I have not observed in any other species, and which 
Michaelsen has not mentioned, is the presence of a series of sacs 
attached to thesepta. These are disposed in pairs and have the ap- 
pearance of solid white bodies attached to the anterior septum of 
each segment, and hanging freely in the interior of the segment. 
They commence about the twentieth segment, and the first few 
pairs are commonly larger than the rest ; they occupy all the 
segments lying behind the twentieth. These peculiar bodies 
suggest egg-sacs and sperm-sacs; they are rather larger than 
the former and smaller than the latter. Structurally they are 
merely outgrowths of the septa containing a spacious cavity 
which communicates by an aperture with the cavity of the 
segment in front ; in their structure, therefore, they agree with 
the egg-sacs. The peritoneal epithelium covering these sacs 
was rather better developed than elsewhere upon the septum ; 
these cells when stained with iodine assume a mahogany- brown 
which fades when the tissue is warmed, but reappears on cooling, 
indicating therefore (?) the presence of glycogen. The glycogen 
appears to be formed in the peritoneal cells of the septum 
generally as well as in those which cover the septal sacs. I 
could not find any trace in the muscles of the septum, and so can- 
