46 



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

 muscle fibre, and nerve, and contains large blood spaces. 

 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, llius 

 enabling the animal to riM-ognise it in some wav, and so 

 subserve the "homing" faculty. When the animal 

 ''shuffles" lound on ihe scar on returning from an excur- 

 sion ihey are in active use. 



CnurLATOKY OkOAXS AM) CcRLOM. 



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 hfemocade, 

 consisting of blood spaces, and the coelom is reduced 

 to the pericardial cavity, which is, therefore, not a l)lood 

 space. The l)lood is a colouiless fluid in which float 

 amoeboid corpuscles. The parts concerned in blood 

 circulation are tlie Heart, the Arteries, and the irregnilar 

 Blood Spaces. 



The Heart may be described as a specialised portion of 

 the hremocoele, which has projected itself into the coelomie 

 space called the pericardium. 



In the primitive Chiton, therefore, the feebly differen- 

 tiated heart is surrounded by coelomie 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 tlie coelom in an infolding of the lining of that cavity. 

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

 pericardial roof, but the connection is not so regular and 

 complete as in (liiion. In most Gastropods, this connec- 

 tion lias (lisa[)|)eared, and it is even possible that it is a 



