No. 420.] HISTORY OF STICHOSTEMMA. 977 
on the two sides of the head. Variation in the number of 
pigment spots can often be observed in a single individual. 
One or more of the spots may divide, or in some cases a num- 
ber of small masses of pigment appear in place of a single 
pigment spot, in consequence of a kind of fragmentation. 
One of these smaller masses may increase to the size of the 
whole, while the others disappear. Migration of these masses 
is often observed. A more complete account of these obser- 
vations is reserved for a future time. 
The body of the worm is very transparent. The alimentary 
canal, blood vessels, terminal nephridial organs, nervous sys- 
tem, gonads, the rhyncoccel, and the proboscis, with principal 
and accessory stilets, can be clearly seen in the living animal 
under slight pressure. For some time past I have employed 
the form for class work on account of the ease with which 
its internal anatomy can be studied. 
The points of difference between this form and S. et/hardi 
as given by Montgomery (96) are as follows: (1) The absence 
of the supraoral sense pit, which suggested the specific name 
“asensoriatum.” (2) The cephalic gland is not as voluminous 
as in S. ei/hardi, and has not one main efferent duct, but the 
ducts of the individual gland cells penetrate the body epithe- 
lium independently of one another, in the manner of subcu- 
ticular gland cells; the external openings of these cells lie at 
the anterior end of the head. The want of a main efferent 
duct, formed by the fusion of the individual cell ducts, might 
be explained by the absence of the supraoral sense pit, since 
in most metanemerteans the main duct discharges at the base 
of this pit. (3) The pigment of the body epithelium occurs 
exclusively in the supporting cells and is not found at all in 
the interstitial tissue. (4) Those gland cells corresponding to 
what I have termed “gland cells 3” in S. ei/hardi are not 
egg-shaped, as in that species, but have an elongated narrow 
form; in structure and in their color reaction to stains they 
show a close similarity to the cells of the cephalic gland: 
thus, they stain intensely with hematoxylin, and with the 
triple stain of Flemming (safranin, gentian violet, orange G) 
combine with the safranin and not with the violet. (5) The 
