136 COMMISSION OF CONSERVATION 



22. They occur first in August. 



23. Normal fixation takes place when the shell of the larva has reached 

 a length of about -38 mm. and is in the umbo stage, not, as was formerly- 

 thought, in the smaller and younger straight-hinge stage. 



24. A probable explanation of the method of fixation is given. 



25. A metamorphosis occurs immediately after fixation through loss 

 of larval organs, as velum, foot, eye-spots, otocysts, cerebral and pedal 

 ganglia, etc., and a development of permanent organs, as spat-shell (dis- 

 soconch), outer hemibranchs, palps, etc. 



26. The age of the chief stages has been determined approximately 

 by fixing the time of the chief events, as spawning, swimming of the trocho- 

 phore, appearance of straight-hinge shell, umbo stage, spatting, sexual 

 maturity. 



27. An accurate system of measurements has been introduced, and 

 a comparison of actual sizes at different changes of habit or of structure. 



28. Size is a more useful criterion than age, since organization ad- 

 vances with growth in size, which depends more upon temperature and 

 food than upon age. 



29. Sections of both larvae and spat have been prepared and studied. 



30. Important organs, as the intestine, gills, etc., have been followed 

 through both larvae and spat. 



31. Development has been traced to adult sizes. 



32. Cross-fertilization between two of the most divergent varieties 

 (Malpeque and Caraquet) was accomplished. 



33. Free-swimming larval, creeping, or fixed stages of the commonest 

 accompanying allied bivalves have been identified and distinguished 

 from those of the oyster. 



34. The physical conditions of oyster beds in different situations 

 have been compared. 



35. The temperature and other conditions for breeding have been 

 determined. 



36. The time of spawning has been narrowed down to a more definite 

 part of the year and to a briefer period than was formerly thought. 



37. The free-swimming period has been limited to the month of the 

 year, and the duration of the time. 



38. The time of spatting has likewise been determined as to month 

 and duration. 



39. The importance of the larva and of the larval period has been 

 recognized. 



40. Since the free-swimming larva precedes the fixed spat, then a 

 systematic microscopic examination of plankton collections may be em- 

 ployed practically to determine when, for any area and for any year, 

 the masses of larvae will first reach maximum size and be ready to become 

 fixed as spat, i.e., when is the best time to put out cultch. 



