220 Transactions of the Royal Microscopical Society. 
adopts in the ordinary method — perpendicular, that is to say, to 
the line of vision as you look straight into the pellet organ ; the 
result is that the sphere which is pushed over in the cup to the 
side where there is no additional supply coming in, is increased by 
addition only on the other side to which accretions do arrive, and 
thus, while one part remains unaltered and spherical, the other 
part, as before, becomes cylindrical, and the same result is finally 
arrived at ! 
When we pass on to the act of depositing the pellet on the 
wall of the building we find the machinery equally specific and 
definite. The obvious remark will occur to the reader that when- 
ever the pellet is made in the attitude last described, and trans- 
versely to the mouth of the pellet organ, it has to be turned half 
round before it can be deposited, while it must be borne in mind 
also that there are two ways of doing this, and that one way is 
right and the other wrong ; for the spherical outline of the bullet 
is always laid on the outside of the case, and the flat end of the 
bullet is always laid to the inside. In the process of depositing it 
the pellet is pinched or nipped between the main chin above the 
pellet organ and a nob or protuberance like an inverted nose or 
second chin underneath that organ (see the diagram) ; between 
this protuberance and the main chin there is a certain amount of 
play, for they can draw towards each other so as to hold the pellet 
when extruded from the pellet organ. But then there comes this 
question : how does the animal know where to lay a new pellet ? 
On this point I cannot agree with those writers who say that the 
pellets are laid irregularly ; on the contrary, as a rule I found 
them laid with great regularity, and one row is seldom or ever 
begun until the previous row is finished, and it is the exception 
arising from confusion in confinement when the pellets are placed 
irregularly. Every little youthful housekeeper begins her domestic 
life by surrounding herself with a girdle of pellets, all laid on the 
top or edge of her transparent case, and she always finishes the 
first row before she begins the second, and Mr. Cubitt, in his 
admirable drawing,* has in no way exaggerated the exquisite 
regularity of the tube when completed. Mow I agree with that 
gentleman that the organs which he calls the “ lips,” but which I 
should call “ hooks,” or spines, and which with the two long 
antennae, or setse-bearing tubes, form such prominent objects as the 
animal rises from its case, Fig. 6, do play some part in connection 
with the laying of the bricks, hut as to what that part is seems 
very uncertain. But there is another organ which he does not 
mention, and which in my opinion plays a much more definite part 
in settling the important question of where the bricks shall be 
laid. That organ is a small pimple-like protuberance armed with 
* ‘ M. M. J.,’ vol. v. p. 209. 
