38 COMMISSION OF CONSERVATION 



12th, at Richibucto. Full grown larvse of 55 x 50 occured first at Bay 

 du Vin on Aug. 5th, from which it may be understood that the free- 

 swimming life of the larva continues for at least two weeks after it has 

 reached the shell-bearing stage. 



Literature on the Larva 



Brack (1690), who was perhaps first to use tha microscope in the study of the 

 young of oysters, distinguished two stages of development within the shell of the mother 

 (of the European oyster) : (1) white, somewhat spherical, quiescent eggs, and (2) white, 

 round, compressed eggs with valves and spiral movement (evidently what we would 

 now call larvse). 



Leeuwenhoek (1695) observed young oysters (also taken from the parent), that 

 moved about rapidly in the water by means of small organs projecting from their shells 

 and which they drew in when they died (the velum). 



Davaine, Lacaze-Duthiers, Coste, de la Blanchere, Gwjti Jeffreys, Savmders, Salen- 

 sky, Mobius, Horst and Huxley all observed the larva of the European oyster, taken 

 from the parent. 



Huxley (1883) states: "During the summer and autumn months, from as early as 

 May to as late as, or even later than, September, according to circumstances and the 

 depth of the water in which the oysters live, which appear to be most influential, a certain 

 proportion of the oysters in an oyster-bed pass into a peculiar condition, and are said by 

 the fishermen to be 'sick.' In about half of these sick oysters a whitish substance 

 made up of innumerable very minute granules, embedded in and held together by a 

 sort of slime, collects in the infra-branchial chamber, filling up the interspaces between 

 the mouth and the gills, and between the gill-plates themselves, and even occupying 

 the vestibular cavity so completely that it is difficult to imderstand how the processes 

 of breathing and feeding can be carried on. 



"This granular slime is what is known as 'white spat' and the granules are the 

 eggs of the oyster. By degrees the granules become more or less coloured; and the mass 

 acquiring a brownish hue, is termed 'black spat'. This change depends upon the de- 

 velopment of the young, which acquire a certain degree of coloration, within the eggs. 

 At the end of a period, the length of which varies with the temperature of the water and 

 other conditions, but appears rarely to exceed a fortnight, the mass of black spat breaks 

 up, and the young, hatched out of the eggs, leave the mantle cavity of the parent in 

 which they have been thus incubated. They become diffused through the water and 

 swarm in vast multitudes at the surface of the sea. 



"A single full-grown oyster produces, on an average, about a million of these free- 

 swimming young or larv£B. If a glass vessel is filled with the stratum of surface water, 

 in which the larvae swim, and held up to the light, it will appear full of minute particles- 

 only l/150th of an inch long, and therefore just visible to the naked eye — which are in 

 active motion." 



Huxley gives a good diagrammatic figure (his Fig. 3) of a straight-hinge larva. 



Horst (quoted from on pages 27, 30), whose earlier work preceded and later work 

 followed that of Huxley, also figures a yomig straight-hinge stage, and both his and 

 Huxley's measurements agree with the earlier statement of Mobius (1S87) that "the 

 young oysters leave the mother when the}' have reached a size of 0-15 to 0-18 milli- 

 meter." 



In America the method of procuring young developing stages, extending from 

 naturally fertilized eggs to straight-hinge larvae, as practised upon the European parent 

 oyster, is not possible. On this account another method, that of artificial fertilization 

 and culture, has been developed by Brooks, Ryder, Winslow, Rice, Nelson and others. 

 The eariier references to this method are all too brief and scattered. Its possibility 

 on a small scale is an embryological feat of great interest and importance. It is an easy 

 matter to raise up larvis to the corresponding stage of structure known to European 

 embryologists. 



Brooks has been already referred to (pp. 3, 21, 24 et seq., and 30). 

 Ryder's papers are not easy to correlate on account of little discrepancies in measure- 

 ments or magnifications, age and occurrence, a variable use of the terms embryo, larva, 

 etc., and involved or ambiguous statement. They all seem to depend upon his experi- 

 ments, along wth Colonel McDonald, at St. Jerome creek, Maryland, June 24, 1882, 

 (1882, p. 383). "The most remarkable result obtained was the apparent fixation of 

 the fry to the sides of the glass hatching vessels twenty-four hours after impregnation." 



