THE ATTACHMENT OF OYSTER LARY/E. 145 



8.35 P.M. the larvae were describing circles a little over i mm. in 

 diameter. As they continued moving around the radius of the 

 circles was gradually diminished, until at 8.46 the first larva 

 came to rest With the foot extended to about one half its full 

 length, its distal end flattened in contact with the glass, the 

 larva swung the body until the foot occupied the median posi- 

 tion, with the left valve against the glass and inclined to it at 

 about 30 degrees (Fig. 2). In this position the ventral edge of the 

 It It valve almost touches the substratum. 

 The ventral border of the mantle was ex- /^Z^*vr |v 



tended until it came in contact with the 

 glass \\here it remained for 2 minutes, and 

 then was \\ithtlrawn. The foot, with its 

 (ilia beating very feebly, was then slowly 

 drawn in, and II minutes after the larva 

 ceased circling the f(KJt had entirely dis- 

 appeared between the valves, and fixation 



FIG. 2. The PC 



was accomplished. The method of attach- taken by an oyster 

 merit of the larva? on the upper and on the larva du"K fixation, 

 lower side of the glass was the same; it 



/, foot; /. r., umbo of 

 illustrates, in the case of those larva' attach- Jc f t V ai\-c; m. mantle. 



ing from below, the power of the foot in 



holding the left valve firmly against the substratum while fixation 



is being effected. 



The great importance of the foot to the ful n oyster larva 



was recognixed by Stafford '10, who described it- n t pin.^ move- 

 ments. The manner in which the larva cement- it -elf fast was 

 deduced by him ('13, p. 65) solely from hi-toloijr.il evidence. 

 He concluded that the mantle could not furni-h material in 

 sufficient quantity nor rapidly enough t" IT of u-e .1- the organ of 

 fixation. As he says: 'The usefulness of the foot .is an organ 

 of locomotion, as a clinging organ, as an or^.m of hvition, had 

 appealed to me for some time but I li.nl no dim t -\ idence to 

 support the view that it was really the ot;<an of final attach- 

 ment." 



Stafford found that a large part of the ki-e of the foot of a 

 lull-grown oyster larva is occupied by the byssus gland which 

 consists of three lobes communicating with a duct which opens 



