VIII 



SUMMARY OF OBSERVATIONS AND DISCOVERIES 



The discoveries, observations, advances, generalizations, or applica- 

 tions of most importance made in the course of this work are: 



1. The first systematic application of the plankton net in the search 

 for and obtaining of oyster larvae. 



2. The first recognition of the older stages of the larva of the oyster. 



3. Oyster larvae can be found in the water about oyster beds. 



4. They are almost confined to the months of July and August. 



5. They may be taken at the surface and at various depths below 

 the surface. 



6. All stages from the freshly fertilized egg to the full-grown larva 

 are suspended in the water or lying on the bottom. 



7. The stages hitherto unknown, constituting the "blank" referred 

 to by Jackson, that could not be raised from eggs by artificial fertilization 

 and culture, are most conspicuous in the plankton, and it was due to 

 lack of plankton study that they had remained unobserved. 



8. The free-swimming period is considerable — close on a month — not 

 one or even six days as had been thought. 



9. The larvae swim suspended in the water, or sink and rest at the 

 bottom, feed, and grow from a length of -062 mm. to a length of -386 mm. 



10. During this time they pass through a shell-less, a straight-hinge, 

 and an umbo stage. 



11. The larval shell (prodissoconch) is asymmetrical, as is also to 

 some extent the contained body. 



12. A probable explanation of the asymmetry is given. 



13. Ctenidial axes and lower filaments of inner hemibranchs are 

 present in the older larvae. 



14. Pigment spots (eye-spots) are present. 



15. The otocysts contain otoconia. 



16. A foot, homologous with that of Molluscs in general, is present 

 in the older larva (simultaneously with the velum). 



17. A byssus gland is present. 



18. Cerebral, pedal, and visceral ganglia are present. 



19. In locomotory organs, nervous system, and sense organs, the 

 full-grown larva has a higher organization than the adult oyster. 



20. The first recognition of the very young stages of Canadian spat. 



21. Spat are found attached to shells, stones, etc. 



