8 Moll 
MOLLUSCA. 
Anatomy and Physiology. 
Huxley discusses the Mollusca in his valuable Manual of the anatomy 
of invertebrated animals, 1877, pp. 470-542. 
L. Fredericq discusses the physiology of Octopus vulgaris. According 
to him, its blood amounts to about one-twentieth of the weight of the 
body, it is blue, salt in taste, but less bitter than sea -water, and con- 
tains colourless globules, which agglutinate together when taken 
out of the body; but it appears that there is no fibrin in the blood. 
Analyses of the blood are given. The heart beats about thirty-five times 
to the minute ; its movement is retarded by electric irritation of the 
visceral nerve which follows the vena cava, and accelerated by section of 
the same. The blood passes from the arteries to the veins by true 
capillary vessels, not by lacunae. The renal organs do not serve to 
convey water from without into the interior of the body, as has been 
supposed by former authors ; chemical analyses of their secretion are 
given. The centre of the respiratory movements is in the posterior part 
of the infra-cesophagean ganglion ; they are not accelerated by obstacles 
to the normal circulation of the blood, as in the Vertebrata, but only 
retarded. The change of colour by the chromatophores is a case of 
mimicry, but depends on the pallial nerves ; their section paralyses the 
dilator muscles of the chromatophores and renders the animal pale ; 
irritation darkens its colours by expansion of the same ; intense light 
paralyses them also temporarily. The secretions of the salivary glands 
and that of the liver are distinctly acid ; the former containing no diges- 
tive ferment, but the latter dissolves fibrin and changes amidon into 
glycose, it therefore resembles the pancreatic fluid of the Vertebrata. 
The nervous string in each arm of the Cephalopoda is a centre for reflex 
movements, in the same manner as the spinal marrow in the Vertebrata^ 
and these movements show the character of’ protection and defence, like 
the movements of a decapitated frog. The muscles contain much taurine, 
but apparently no gly cogene. Arch. Z. exp4r. vii. pp. 635-583. 
M. Furbringer has microscopically examined the cartilages in the 
head of the Cephalopoda, and states that their structure more resembles 
that of the bones of the higher animals than hyaline cartilage. Morph. JB. 
iii. [1877] pp. 456-458, with a woodcut. 
1 . Muscular System and Movement. 
H. Sim ROTH has examined the manner of creeping in Limax cinereo- 
niger (Wolf), Arion ater (L.), dindi Helix pomatia (L.) ; he distinguishes 
two systems of fibres within the foot, those which he calls locomotive, or 
extensile, are the true active part during creeping, but they act by exten- 
sion, not by contraction, and can only do so when the lacunae within the 
foot are filled with blood; they begin their activity only when excited by 
the influence of the pedal nerves, but continue it independently of the 
nerves ; their extension causes the undulating aspect at the lower side of 
the foot ; they are all disposed in the longitudinal direction and move the 
