4. On Variability in Development. By Professor A. Mitnes MarsHatt, 
F.R.S., and KE. J. Buss. 
TRANSACTIONS OF SECTION D. 861 
5. On Secreting Cells.1 By Professor G. Ginson. 
During some years past the author has been engaged in studying the structure 
and mode of action of secreting cells. For, with respect to the question of secre- 
tion, it seems to him that, though an immense number of works have been published 
on the subject, there remains still much that is unknown. 
A complete and adequate summary of these still unfinished researches is not 
given, the author confining himself to a very short account of the principal results 
. obtained by describing in a few words several of the most interesting objects which 
he has met with in different groups of beings. 
: (1) The silk-producing cells of the Lepidoptera.—The author made a short com- 
munication on the secretion of these cells last year, at the Newcastle meeting. On 
that occasion he pointed out that these cells are perfectly closed elements, their 
inner surface being covered with a thin but very strong and finely striated 
membrane. 
The silk substance, produced within the protoplasm, passes from it into the 
cavity of the organ, not by forcing its way violently through this membrane, but 
by filtering through it slowly and regularly. 
(2) The epithehal cells with a striated plate—These cells are well known to 
biological students ; but many are not aware of the degree of development to which 
this striated plate may attain in several inferior animals, especially in the 
arthropods. 
There exist two kinds of striated plates, which shall be distinguished as the 
open and the closed. 
The former is composed of tiny rods only, very regularly disposed on the inner 
surface of the cell, and entirely separated from each other. The cells bearing this 
plate resemble so closely ciliated cells that one is apt to mistake one for the other; 
but in the striated plate the tiny rods never move, and so in spite of their likeness 
and morphological homology they are not real cilia. 
These motionless rods are ordinarily glued together by a sticky matter, which 
conceals them more or less from sight. But often, as happens particularly during 
digestion, they are entirely free from this matter, and then they appear exactly 
like cilia. It is thus scarcely necessary to say that there is no question of tubes 
piercing the plate, and that therefore Professor Leydig’s denomination, ‘ Poren- 
kaniilen,’ is by no means to be retained with respect to the strive. 
Very striking instances of this kind of plate are found in the intestine and Mal- 
pighian tubes of insects, myriapods, and crustaceans. In vertebrates this plate 
is well known in the digestive organs. It exists also in the kidney, for the so-called 
‘ Heidenhain’s rods’ are nothing else than the rods of an open striated plate covering 
certain cells of the urinary tubes. 
In the closed plate, on the contrary, the rods or cilia are united to each other 
by transverse fibres, and its external surface seems to be closed with an extremely 
thin’and apparently structureless membrane, Its structure does not differ from 
that of many other cellular membranes. 
Certain parts of the intestine of insects and crustaceans are covered with these 
closed plates ; but in certain species, for instance in the Oniscus, the digestive tube 
_ does not contain a single open plate. 
(3) The silk-producing cells of Tenthredo—The silk-producing gland of this 
species differs notably from that of the silkworm. It consists of an epithelial tube 
with many large appendicular cells. These are the producing elements. They are 
acked with silk spherules that fuse together into a more considerable mass, which 
glides directly into the tube through a yawning aperture. In this case the secreted 
substance does not filter through a membrane. 
oe 
1 This work when published in extenso will contain a summary and a criticism 
of the literature of the subject. 
