HISTOLOGY OH THE LAND-PLAN ARIANS OE CEYLON. 
119 
probably assist the muscular movements in the act of progression. Max Schultze ( loc . 
cit. 4, p. 34), though he did not see the cilia in Geoplana , yet concludes that it must be 
covered all over with them from the experiments of Fr. Muller (p. 23), who covered 
the body of one of these Planarians with arrowroot, and observed a motion of the 
particles which seemed to show the presence of cilia. Darwin came to the same result 
from the observation-of the motion of air-globules in the slime of Geoplana. Mecznikow 
found the skin of Geodesmus bilineatus covered with cilia. The alteration in structure 
of the epidermic layer where it carries the strong ambulacral cilia is remarkable ; there 
axe no rod-like bodies or gland-cells at all in this region, which seems to be entirely 
devoted to the production and working of the cilia. 
Basement Membrane. — The epidermic elements in Bipalium rest on a very fine base- 
ment membrane, homogeneous in structure. The basement membrane is, in transverse 
sections of the body, with difficulty to be seen as a structure separate from the external 
circular muscular coat which lies immediately beneath it ; but in favourable prepa- 
rations it is easily distinguished by its much deeper staining with carmine (Plate XI. 
fig. 1, B). In longitudinal sections the external circular muscular coat is seen in section, 
and then the basement membrane stands out in considerable relief (Plate XV. fig. 9, B). 
This basement membrane is not to be confounded with the thick membrane often 
described as such in Nemertines and Planarians, and which, as will be seen further on, 
is the homologue of the external circular muscular coat. The basement membrane is 
perforated for the discharge of the secretion of the subcutaneous glands and the passage 
of the rod-like bodies, the parent cells of which are situated beneath it. A definite 
basement membrane could not be detected with certainty in Bhynchodemus. 
Subcuticular Begion. — Immediately beneath the basement membrane is the external 
muscular system, consisting of a circular and longitudinal series of fibres, which will be 
considered under the heading “ Muscular System.” Beneath this system, again, is the 
zone of loose tissue before referred to, which is occupied by fibres continuous with the 
radiating muscular fibres of the body, which form a loose stroma, in which are situated 
the parent cells of the rod-like bodies, a large quantity of glands, the pigment, and also 
the eye-spots, which latter will be most conveniently considered with the nervous 
system. The parent cells of the rod-like bodies (Plate XI. fig. 1, B G) are arranged 
beneath the external longitudinal muscular layer at a tolerably even depth ; they are, in 
spirit specimens, of an elongated oval form, with the upper extremity drawn out to a point 
or long filament, which in some cases may be seen to reach up to the basement membrane. 
In spirit specimens they assume various forms (Plate X. figs. 11 & 12) ; and I was at first 
led to believe that they actually contained dart-like bodies like those described by 
Mecznikow in Geodesmus bilineatus (loc. cit.), which he calls “ Nessel-Organe,” which 
he found in vacuoles in the animal’s skin, which seemed to be shot out when the 
animal was pressed under the covering-glass, and which were developed in glands beneath 
the epithelial layer. But after more careful observation, and especially comparison of 
the corresponding organs in Bhynchodemus with those of Bipalium , I came to the con- 
