36 Moll. 
MOLLUSCA. 
5. Respiratory System. 
In Poromya , Silenia , Smith ( nec auctt.), and Cuspidaria , there is a 
muscular partition extending from one adductor to the other. This has 
been, hitherto, taken for the body-wall, but is formed by the modified 
gills. This arrangement is found carried out to a less extent in Lyon- 
siella. These constitute a special division ( Septibranchia ) of the Pelecypoda 
containing the families Cuspidariidce, and Poromyidce. The general 
morphology of Pelecypod gills is discussed, and a phylogenetic interpre- 
tation proposed ; Pelseneer (3). 
; Priority is claimed in respect of some of these observations, and correc- 
tions are made of others ; Dall (2). 
Ampullaria has both a lung and a gill ; two kidneys are present, of 
different structure, also a pyloric caecum ; for peculiarities of genital 
organs, vide p. 37, infra ; Bouvier (5). 
Experiments on the porosity of the septum of Rumina decollata and 
the shell of Cyclostoma elegans ; Folin (1). 
Ancylus fluviatilis possibly takes in minute bubbles of oxygen from the 
plants on which it feeds ; Gain, 
6. Excretory and Secretory Systems. 
An important account of the situation, occurrence and histology of the 
pericardial gland of Pelecypoda is given, from which the following con- 
clusion is drawn. Numerous Pelecypods have a gland developed from 
the pericardial epithelium. It arises (a) above the auricles, (b) in the 
anterior angles of the pericardium : (a) occurs in Arca ) Pectunculus, &c. t 
becomes degenerate in the Monomyaria ; (b) occurs in Unio, Venus , 
Cardium , &c., and Dreissena. In Pholas arrangements occur which are 
repeated in Area , , Pectunculus , and Lithodomus. The prominent frills 
of Meleagrina are peculiar. Concretions occur iu some instances, which 
are probably evacuated through the kidneys. The function of the whole 
gland is excretory. A number of collateral conclusions are also enun- 
ciated ; Grobben (1). • 
The organ of Bojanus of Pelecypods and its secretion have been 
minutely studied; the latter contains neither uric acid, urates, nor 
hippurio acid, but urea is present in it ; Letellier. 
In certain Prosobranchiata a portion of the kidney differs in structure 
from the rest, being in fact a closed diverticulum of the circulatory 
system ; perhaps it is a blood-gland ; Perrier (3). 
The renal secretory apparatus of Littorina littorea consists of a series of 
lamellae, one edge of which hangs freely into the renal cavity. The 
glandular epithelium consists of two kinds of cells, glandular and ciliated. 
The excreted materials collect iu a vacuole in the glandular cell, which 
falls out into the cavity when it reaches a certain size. The glandular 
tissue of the kidney does not extend to the pericardium : Perrier (1). 
These observations confirmed and extended to different genera ; 
id. (2). 
