LARVAL OR SvMMMING STAGES 31 



not been described in the European species, and all our attempts to obtain it in our owoi 

 species bave failed. In artificial confinement the oyster dies at this stage." 



Nelson (1901 p. 310) "The fry, after about five days, develop a two-valved shell, 

 and then they seek a place to settle down on." 



Nelson (1902 p. 333) "These eggs rapidly develop into small, free-swimming fry, 

 that in a few days are provided with a bivalved shell; and then they settle down on a 

 clean surface, of a shell or stone, etc., to which they become attached by the left side." 



The foregoing quotations acknowledge that there was a limit to 

 which the development of the oyster had been continuously observed. 

 The figures by Brooks, Horst, Huxley, Ryder, Jackson and Nelson were 

 very near to the young straight-hinge stage I have just described (Plate I, 

 fig. 12; Plate V, fig. 26) and represented the oldest larvse known. The 

 next stages known were fixed stages (spat), of much larger size and dif- 

 ferent shape (about the same as my Plate I, fig. 22) . Between the two was 

 a period of unknown duration — the 'gap' of Brooks, the 'intervening 

 period ' of Horst, the ' locomotive state ' of Huxley, the ' unbridged ' inter- 

 val ' of Ryder, the ' blank ' of Jackson. Brooks was not inclined to specu- 

 late beyond the facts of his observations. Winslow believed that the 

 oyster larva was predisposed to fix itself very soon after segmentation. 

 Ryder thought it might do so in 24 hours. Rice mentions 2 days, Nelson 

 5 days. Huxley had kept larvae for a week. Rice for 14 days, Lacaze- 

 Duthiers for 30 and even 43 days without apparent change. This be- 

 haviour in confinement must be different from what it is in the open 

 water of the sea, but what the latter might be nobody knew. 



Plankton.*— This was the condition of the subject when in 1904, 

 I began my work at Malpeque, although at the time I had little 

 knowledge of what had been done or remained to be accomplished. 

 What I undertook was to gain some first-hand practical information 

 about the breeding and embryology of the oyster in one of our own northern 

 oyster areas; and I am sure nobody has been so much surprised as myself 

 that, in the course of one short season, I had the good fortune to deter- 

 mine the time, place and manner of all the important events in the de- 

 velopmental history of our oyster, to add a new chapter to the litera- 

 ture of the subject by filling up the gap referred to by Brooks, the 

 unbridged interval of Ryder, or the blank of Jackson, and, along 

 with my subsequent researches, to furnish abundant data for a clear 

 perspective of the complete ontogeny of the oyster. Important as 

 this is from the standpoint of morphological and theoretic zoology, 

 it is perhaps surpassed in value by the light thrown on economic 

 problems and methods of oyster culture. Artificial methods of breed- 

 ing oysters in a small way had succeeded, as we have seen, in 

 the hands of a few practical zoologists only in bringing the young 

 to a free-swimming stage of little over .069 mm. (= 1/360 inch), 



*Plankton, a term applied collectively to all those minute animals and plants 

 which swim or float about in any of the great natural bodies of water. 



