[15 J DEVELOPMENT OF THE OYSTER. 905 



ail aquarium. . I am not able to say anything positive in regard to the 

 duration of the period which elapses from the time when the larvce be- 

 come free to the time when they become fixed ; nor do 1 know what 

 changes they undergo during this period. We have not succeeded 

 either in producing a further development of the oyster larvae, nor in 

 securing their fixation, even in aquariums where there was a constant 

 current of sea- water, or in those through which a continuous current of 

 air was passing.^^ I have also been disappointed in my attemj)ts to 

 procure oysters in these phases of development by means of catching 

 larvfe floating about in the sea. Although I have several times fished 

 in the neighborhood of places containing collectors, by means of a trawl 

 net, and obtained many different larvte of auuelides, crustaceans, ascidi- 

 ans, i&c, I only once succeeded in capturing some oyster larvae, although 

 they doubtless move about freely in the sea for several days. We must 

 consider the account of Engineer B. de la Grye^" as fabulous, as he 

 states that an oyster cultivator of the river Auray, after having squeezed 

 the spawn from an oyster, smeared it on a stone which he immediately 

 threw into the water, which stone soon became covered with oysters. 



If one compares the most highly developed larvae, described above, 

 and the youngest among those which have become fixed, great differ- 

 ences in their organization may be observed. At first the shell grows 

 very rapidly, for while it only measures O.IG millimeter in height in a 

 larva which is on the point of leaving the mother oyster, it measures 

 more than 0.24 millimeter in the smallest of the fixed shells. The 

 adductor occupies another place in the larva than in the fixed animal,^^ 

 while in the fixed animal this muscle is found on the mouth side of the 

 intestine, and therefore in the place of the posterior adductor of the 

 Bimyaria, in the larva it is found in the ab-oral region (the hemal side, 

 of Huxley) of the esophagus, or in the position of the anterior adductor 

 of the Dimyaria. It is, therefore, probable that the adductor of the 

 larva is homologous with the anterior adductor of the Dimyaria. The 

 velum also disappears during this period, while on the other hand the 

 branchiae may be observed to grow. As shown by the drawing of a 

 larva in a later phase of development (Fig. 19), the branchiae are at first 

 formed by filaments which are separate along their entire length, ex- 

 cept at their bases and at their tips, where they are joined to each 

 other. The branchiae of Ostrea edulis, therefore, develop as De Lacaze- 

 Duthiers also supposed,^- in the same manner as those of the Mytilus 



^^These experiments were made in conjunction with Dr Leo de Leeuw. In order 

 to pass air through the water, I used the apparatus recommended by Mr. Fol for 

 journeys. This apparatus is composed of two petroleum cans (tin), provided at the 

 top and bottom with a spigot, and joined by a rubber tube. One of the cans, filled 

 with water, is placed at a certain height ; from it the water ruus into the lower can, 

 drives the air out of it, and causes it to pass through the aquarium. 



^oH. de la Blanchfere: Industrie des Eaux, p. 150. 



»' Professor Huxley called my attention to this fact in a letter to me. 



^- Memoire stir le dtveloppement de iranchies. In Ann. des. Sc. Nat. 4™<' s6: Zoologie, 

 vol. V, p. 43. 



