50 Gardiner and I to. — On Mucilage-cells 
representatives of the Animal and Vegetable Kingdoms great 
caution must be observed. But we are nevertheless of opinion 
that a distinct unity both of plan and structure underlies all 
the similar phenomena common to the two great classes which 
constitute living beings, and that any apparent difference is 
one of degree and not of kind. In the case of certain animal 
glands, e.g. serous and mucous salivary glands, Langley 
concludes that the protoplasm forms the hyaline substance, and 
then out of this manufactures the granules which, during 
secretion, are turned out of the cell and give rise to the 
particular substance which the gland happens to secrete. 
The state of active secretion is followed by a period of rest 
during which the protoplasm grows, forms new hyaline sub- 
stance, and from this again are produced new granules. We 
believe that a series of changes essentially similar in character 
obtain in certain plant-cells also. Usually speaking, plant-cells 
are incapable of such active and repeated secretion as occurs 
in those of animals, and in many instances, e.g. Blechnum occi- 
dentale and Osmunda regalis , the secretory changes occur in 
the cell once and for all, and at their termination the cell dies. 
But in other glands, e.g. those of Drosera , it appears exceed- 
ingly probable that the phenomena which accompany the 
repeated secretion are quite identical with those which happen 
in so many animal glands. 
We have seen that, in the two mucilage-glands investigated 
by us, the secretion is not turned out of the cell during its life- 
time, but in such cases as the resin-glands of Blechnum occi- 
dental , where the secretion normally escapes, we may en- 
deavour to offer some explanation as to the way in which 
the passage of the secretion to the exterior is brought about. 
For this purpose we may conveniently divide the secretions 
into (i) soluble and (2) insoluble substances. The soluble pro- 
bably simply pass through the substance of the protoplasm 
by diffusion, but we must not omit to state that during this 
process the external membrane (hautschicht), the ectoplasm, 
must undergo some decided modification or change in relation 
to such special phenomenon. The insoluble secretions on the 
