46 



core of the tentacle is a loose network of connective tissue, 

 muscle fibre, and nerve, and contains large blood s])aces. 

 The above described arrangement of the muscle fibres 

 of the pallial tentacles accords well with our supposition 

 as to their nature, for, better than any other arrangement, 

 it allows of their sweeping over the rock surface, thus 

 enabling the animal to recognise it in sonu^ way, and so 

 subserve the " lioming " faculty. When the animal 

 "shuffles"' round on the scar on returning from an excur- 

 sion they are in active use. 



rTECI^LATOrvY (IrGAXS AND CcRr-OM. 



Blood System. — As in Molluscs generally, this is to a 

 large extent lacunar, and is greatly developed at the 

 expense of the coelom, which is reduced to small dimen- 

 sions. The so-called body-cavity is a htcmocade, 

 consisting of blood spaces, and the coelom is reduced 

 to the pericardial cavity, which is, therefore, not a blood 

 space. The blood is a colourless fluid in which float 

 amoeboid corpuscles. The parts concerned in blood 

 circulation are the Heart, the Arteries, and the irregular 

 Blood Spaces. 



The Heart may be described as a specialised portion of 

 the hfcmocoele, which has projected itself into the coelomic 

 space called the pericardium. 



In the primitive Chifon, therefore, the feebly differen- 

 tiated heait is surrounded by coelornic epithelium, which 

 goes up on either side to the dorsal wall of the pericardium, 

 i.e., the heart is, as it were, suspended from the dorsal wall 

 of the coelom in an infolding of the lining of that cavity. 

 In Pafella the heart (ventricle) is also connected with the 

 pericardial roof, but the connection is not so regular and 

 complete as in Chiton. In most Gastropods, this connec- 

 tion has disappeared, and it is even possible that it is a 



