40 COMMISSION OF CONSERVATION 



Combining the statements of his various works in this way, Ryder's views may ap- 

 pear self-evident, but let a reader, imfamiliar with the true history of development of 

 the oyster, try to understand his papers separately and I doubt if he can make much 

 headway. One of the greatest causes for ambiguity arises from the varying meaning 

 of terms, in which Ryder is not the only one to err. "Embryo" may refer to either 

 "embryo", "larva" or "spat." "Larva" may mean either "larva" or "spat." Ryder 

 appears to have considered the building of a new kind of shell (spat shell) arotmd the 

 edges of the larval shell as the mark of distinction between a larva and a spat, and that 

 consequently when a larva first settles down and becomes attached it remains a larva 

 until the spat shell can be detected. In this sense Fig. 3 would represent a larva, and if 

 the animal represented by Fig. 1 were to live and grow imtil it reached the- size of Fig. 

 3, it would throughout this time continue to be a larva. But this is contrary to all 

 zoological understanding of what constitutes a larva; an immature but free-roving and 

 independent stage in the life-cycle of some animal and having different habits and 

 a different form from the adult. The difference may be, and generally is, so great 

 that the larva and the adult would upon first acquaintance be regarded as different 

 species or even as belonging to different classes of the animal kingdom (e. g. a cater- 

 pillar and a butterfly or a tadpole and a frog). The transformation (metamorphosis) 

 of the younger into the older state is not a sudden process, but the change of habit may 

 be and will then form the best mark of division between the two stages. When an old, 

 full-grown, free-swimming or free-creeping, umbo-shelled larva of an oyster first settles 

 down and attaches itself to some object, as a rock or shell, it becomes a yoimg spat, 

 although its organization remains for a time more like that of the larva than like that 

 of a grown oyster. 



Winslow has been referred to (p. 30). 



Rice (1883, p. 28) : "Thus equipped I began work early in July and was able before 

 I left the city to present to the gaze of those interested in this class of bivalve, young 

 oysters which had been kept alive for 14 days, and were at that time apparently strong 

 and healthy. About 44 hours after the ova had been impregnated, one of the young 

 oysters, which had developed so far as to be entirely enclosed by its two shells within 

 the field of the microscope, thrust out a portion of the velmn and finnly secured itself 

 to the glass slide upon which it had been placed." 



Rice divided the life of the developing oyster into three portions: (1) a free- 

 swimming condition ; (2) when covered by a shell, unattached, not capable of moving 

 freely from point to point, except to whirl about, and thus to roll around upon what- 

 ever substance it may rest; (3) attached, including the proboscis stage. 



Jackson, referred to (p. 30). 



Nelson, referred to (pp. 21, 24, 28, 31). 



In the preceding quotations it has been shown how oyster larvae have been ob- 

 tained from the gill-chamber of the European oyster, and how raised f^rom eggs of 

 the American oyster. It may be pointed out here that the third method of ob- 

 taining them conveniently and in vast numbers is by means of the plankton net as 

 first practised in Canada and by myself. The idea had occurred to others but had not 

 been put into practice. My own employment of the plankton net for this purpose was 

 not due to any knowledge of these suggestions for I did not know about them until sev- 

 eral years after I began the practice. At St. Andrews, five years before, and at Canso, 

 three years before, I had used nets to collect other plankton organisms. 



Huxley (1883, p. .53): "It is obviously useless to speculate upon the causes of a 

 'failure of spat,' imtil, by the examination of samples of oysters from time to time, 

 and by sweeping the superjacent water with a fine towing net, the exact nature of 

 the particular case of failure has been ascertained." 



Horst (1884, p. 905) : "I have been disappointed in my attempts to procure oysters 

 in these phases of development by means of catching larvae floating about in the sea. 

 Although I have several times fished in the neighbourhood of places containing col- 

 lectors, by means of a trawl net, I only once succeeded in capturing some oyster larvae, 

 although they doubtless move about in the sea for several days." 



Brooks (1880, p. 57) speaks of his "failure to find any floating embryos in the open 



ocean After the middle of July I found, a few embryos at the surface of the 



water of the Sound." 



Prince (1895, p. 13): " In my investigations upon the Pacific coast, in the Do- 

 minion cruiser 'Quadra,' I captured many small embryo oysters several miles from 

 any known oyster areas." These, if they were oyster larvae at all, must have been of 

 the British Columbia oyster, but it is not stated how taken or how recognized to belong 

 to the oyster, and there is no evidence in the paper to prove that they were not larvae 

 of some of the other numerous bivalves of the British Columbia coast, for at that time 



