152 



ZOOLOGICAL PHILOSOPHY 



and exhibits neither the gangUonic longitudinal cord of the inverte- 

 brates which have nerves, nor the spinal cord of the vertebrates. 

 This is highly characteristic of them, and clearly distinguishes them 

 from the other invertebrates. 



TABLE OF MOLLUSCS. 



Order L — Acephalic Molluscs. 



[First group, Brachiopods ; last group, Tunicates ; the rest, 

 Lamellibranchs. H. E.] 



No head ; no eyes ; no organ of mastication ; they reproduce without copulation. 

 The majority have a shell with two valves which articulate at a hinge. 



