4 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
not permanent or constant. I have elsewhere (1891, p. 23) expressed my 
belief in the homology of the “ Stibchenstrassen” of the Rhabdoccls with the 
cephalic slime glands of Triclads, and a comparison of the sagittal section of 
M. lingua (Graff, 1882, Taf. VI. Fig. 3) with Figure 15 of this paper is strikingly 
suggestive in this regard. Kennel (1888, p. 455) has also shown that in many 
fresh-water Triclads there appears in preserved material a more or less shallow 
groove, or depression, on the vent al surface at the anterior end corresponding 
to a region by which the living animals are able to attach themselves. It is 
the region where the cephalic slime glands open to the exterior. He suggests 
for the ridges at the sides of these ventral depressions the names “ Haftwul- 
sten” and “ Haftlappen.” Grube (1872) has also described similar pits or 
grooves in several fresh-water Planarians. 
The organ in D. lacteum is not a true sucker, nor does the animal employ its 
anterior end for the purposes of attachment to any greater degree than the 
posterior or lateral margins of its body, along the ventral surface of which 
numerous mucous glands have their openings. In truth, it is the margins and 
posterior end that adhere more firmly to a support ; often when the animal is 
forcibly removed from. the side of the aquarium the parts of the margin or the 
posterior end will adhere so firmly to the glass that the points of attachment 
are drawn out into digitate processes. Figures 13 and 14 are from transverse 
sections through the adhesive pit of D. lactewm, Figure 13 being through the 
almost extreme anterior part, while Figure 14 is somewhat more posterior. Both 
sections are from the same individual, — one in which the organ was unusually 
well developed. Figure 15 represents a sagittal section through another indi- 
vidual, and Figure 9 is a surface drawing of an individual killed in hot corro- 
sive sublimate. It will be scen that the region involved in the organ embraces 
all that portion of the hypodermis oceupied by the openings of the mucous 
glands. As already shown by Leydig (1864), the hypodermis which lines the 
depression is devoid of cilia and rhabditi, the latter being replaced by the 
mucous glands, and the transition from one to the other being gradual. The 
exact histological character of the hypodermis lining the depression could not 
be ascertained, the terminal ducts of the glands being so closely compacted as 
to mask all details in this region. In Figures 14 and 15 are seen cross and. 
longitudinal sections of the retractor muscle of the organ, Nothing in the 
shape of a protractor muscle could be discovered, this function possibly being 
assumed by the circular muscles of the dermo-muscular sac. 
The variation in the number of the eye-spots is not a feature peculiar to the 
American form of D. lacteum, as I stated in a previous note (1896, p. 1048), 
for accessory eyes, “ Nebenangen,” have been observed in this species by Car- 
rière (1882, p. 164) and Iijima (1884, p. 438), according to whom they are not 
ave. According to my observations there is in such cases usually one pair of 
eye-spots, corresponding to the normal single pair, which is more prominent, 
than the accessory eye-spots. In what appears to be a closely allied form, Soro- 
celis gutata Grube (1872), there exist two series of eye-spots arranged in the 
form of two arcs ; the number of eyes in each arc is usually seven, but there 
