184 ANATOMY AND LIFE HISTORY OP MOLLUSCA. 



4. The tropical fauna of the Indian Ocean is extended in many- 

 respects far into the extra-tropical portions of the Australian seas. 



5. An examination into some of the principal organs of the 

 Mollusca, such as the Raclula, branchial arrangements, &c, shows 

 that they possess the features which are common to Mollusca all 

 over the world. 



6. The circulatory organs are also the same with haemoglobin 

 uniformly in the circulating fluid in the same portions of the 

 animal. The genera Area and Solen and probably Fasciolaria, 

 have species with red blood as in Europe. 



7. The sense organs in the tegmentum of the shell, which were 

 first discovered by Prof. Mosely in several genera of Chitonidye, are 

 found in many genera of both bivalves and univalves, such as 

 Trigonia, Anatina, Area, Pecten, Venus, Ostrea, Patella, Acmwa, 

 Siphonaria, Cerithium, Turbo, Littorina, RiseUa, and others. 



8. In two species of Trigonia the development of the eyes 

 strongly resembles that of the Ommatidia of insects, associated 

 with sense-organs forming probably the most interesting and 

 wonderful instances of this peculiar endowment. 



9. Associated with these sense-organs large ganglia and 

 dependent nerves are found in the substance of the shell in both 

 univalves and bivalves. 



10. The calcareous opercula of some species contain nerve- 

 ganglia and sense-organs, and probably this is shared by some 

 chitinous opercula to a small extent. 



11. The ganglia in the shell-substance are so much larger than 

 any nervous tissue in the softer parts of the animal, that they 

 are apparently the main sources of nervous influence. 



12. That these ganglia suggest from their position and their 

 multiplicity of sense-organs, that they are really cerebral ganglia. 



13. That the above bivalve species are erroneously described 

 to be acephalous, and that if anything they are better endowed 

 with a head and brain structure than some univalves. 



14. In the mantles of both bivalves and univalves eyes have 

 been found, as well as on the dorsal papilla of some species of 

 Onchidium. 



15. In following the life-history of young oysters, it is found 

 that the ova are nursed in the gill-chambers of the parent, a fact 

 which may have an important influence upon their cultivation. 



16. A similar arrangement is found to exist among certain 

 species of Unio, Siphonaria, Patella, and Acmcea. 



17. In very young Siphonaria, but sufficiently advanced to 

 have all the organs differentiated, the lobe of the mantle in front 

 of the head is found to be covered with from 80 to 90 minute 

 spherical and highly refractive bodies which seem to be sense- 

 organs and may have visual powers. 



