140 
ANIMAL — GLANDULAII AND MUSCULAR SYSTEMS. 
Fig. ‘298. — IClcmenis of liver or iligeslive gl;uid of Ifrii.v 
poviatia^ showing its coniple.v structure, highly niagnificil 
(after Vogt and ^'ung). ch. c. lime cells ; c. ft. cell 
nuclei ; fat globules ; ,/<•/-. c. ferment cells ; granular 
substance; iiz'.c. liver cells ; 7\ vacuolated ferment cells. 
Tlie Glandular or Secretory system is a yeiy important one, not 
only for preserving tlie external integnment in a moist and snpple 
condition by a plentifnl secretion of nincns from tlie innnmerable 
nnicellnlar goblet-sliaped glands scattered beneath and amongst the 
epithelium, but for the elaboration of tbe various ferments and 
secretions necessary for 
digestion and for the 
separation and elimina- 
tion of noxious substances 
from tbe body. 'J'he Liver 
or Digestive Gland is one 
of the largest and most 
important organs of the 
body, and has jirobably a 
com})lex function, serving 
not only as a store- 
house for combustible fatty carbohydrates and a centre for secreting 
digestive ferments, but also contains numerous lime-secreting cells, 
whose jiroducts are said to be utilized iu the formation of the shell 
and epijihragm. The Renal organs or Nejihridia, which are in close 
association and connection with the iiericardium, are very glandular 
in structure, and secrete or eliminate from the blood the waste jiro- 
ducts of the body iu the form of urea or uric acid. The Pericardial 
Gland is also an e.xcretory organ eliminating a still more acrid secretion, 
and, like tbe renal organs, is richly irrigated by the blood system, 
which circulates within tbe organ before entering the auricle. 
Calcareous, Cbitinous, and Pigmentary subepithelial cells of con- 
nective tissue are also })laced in different i)arts of the body, but are 
more especially congregated at the tliickened edge of the mantle, 
where they contribute to the formation and colouring of the shell. 
The iMuscuLAR system is iuHnenced greatly in its character and 
degree of develoiiment liy the presence or absence of an e.xternal 
shell ; its tissue is generally formed by 
smooth, cellular and unstriated band-like 
iiljres, but those muscles callable of raiud 
contraction afford indications of their 
greater differentiation by displaying a 
deceptive appearance of striation sometimes arising from transverse 
rows of granules iierpendicnlar to the axis of the hbre. The muscular 
Fig. 200. — Unstriated muscle-ribre 
from foot of AU’ritina Jlni'iatiUsy 
liighly magnified (after Boll). 
