Morse.] 326 [March 19, 
have no sort of connection with the inner walls of the shell secreted 
by it, from which the shell readily drops. This feature renders 
possible the formation of pearls, by irritating substances or parasites, 
finding their way between the mantle and shell. 
The molluscan shell is never perforated with tubules passing per- 
pendicularly through, from one surface to the other, nor are there 
any minute ramifications of the mantle, or, other portions of the 
soft parts, entering the substance of the shell, and consequently no 
adhesions of the body, save by the special muscles above alluded to.1 
In the Annulata the integument is rarely ever extended beyond 
the limits of the body. When this is the case, it forms a broad 
membrane bordering the thorax, as in Protula, Serpula crater (See 
Plate I., fig. 10), and others, orit surrrounds the head in a collar, 
often everted, split upon the sides and notched in the median dorsal 
region, and separated in a median line below. In Protula Dysteri, 
a broad membrane borders the lateral aspect of the thorax, from 
which the sete spring. In Serpula crater, the membrane borders the 
thorax diagonally, being free at the posterior dorsal region of the thoraz. 
In Brachiopods we have an extension of the tegumentary envelope 
from above and below, enclosing the arms. This membrane is also 
split upon the sides, and is directly to be com- 
pared with the cephalic collar in certain tu- 
biculous annelids, as Sabella, for instance, 
where it differs only in degree. In Sabella 
the cephalic collar does not cover the bi- 
lobed arms, but it is a split upon the sides, 
and notched in the median dorsal line. In 
many Brachiopods there is also a notch in 
the median line, and the genus Pygope of 
: ! Link, the notch divides the collar into two 
sae hias aoe oe lobes, which afterwards unite, leaving a hole, 
a eaten ee ee ROT space in the shell. In other words, this- 
fe RMSBED| RODS membranous collar covers simply the base 
of the arms in those worms possessing it. While in the Brachio- 
1In his work on the Microscope, Dr. Carpenter has described, as peculiar to 
Anomia, an irregular net work of minute tubules, running parallel to the surface 
of the shell, scantily distributed in the inner layers, but very abundant in the 
outer layers. In his last edition of this valuable work, Dr. Carpenter explains 
the character of these minute tubules, and refers them to the action of a parasitic 
fungus. Mr. Mark Stirrup, at a meeting of the Manchester Philosophical Society, 
England, exhibited sections of various shells, and showed that in Anomia, the 
ramifying tubules were produced by a fungoid growth. 
