162 Journ. of the Asiat. Soc. of Bengal. [May & June, 1915, 
of Avicula vexillum, it showed, on microscopic examination, 
distinct traces of incipient ‘‘ finger’’ processes along the edges 
of the growth rings in the peripheral prismatic shell area. The 
marginal area of the shell was more or less greenish in tint with 
distinct radial bands of brown and dark green. 
Off Tirupalakudi on April 28th, stage I was again present 
in the plankton taken both at the surface and at 14 fathom, the 
ship being anchored in 2} fathoms. The numbers were how: 
ever greatly reduced, and it was obvious that no extensive 
fresh spawning had taken place during the fortnight’s interval 
subsequent to April 13th. A few specimens of the more at 
vanced stage II were also seen, exhibiting again free-swimming 
habits, when the water was agitated. 
more important was the capture of a yet further 
advanced stage still retaining the free swimming habit. 
this latest stage (stage III) three specimens in all were taken, 
one in one haul and two ina second. The three averaged 46 
mm. in length, a size hitherto unquestioned as being of wholly 
sedentary habit. ‘On putting them into a small aquarium, ! 
noted, as I have done in Ceylon, their great activity and eager 
ness to crawl up vertical surfaces by means of the foot. One 
made two byssal threads within half-an-hour, exceedingly 
tenuous, but still capable of supporting the body. To testthelr 
power of adhesion I swirled the water round and emptied 
it suddenly. The two that were on the side of the glass at 
tached by byssal threads both lost hold, parting with the rool 
of the byssal cable (which remained attached to the glass) 
stage III, oyster spat readily detach, and move freely on! 
over the sea bottom, and there is now good reason to beh 
that in the presence of a strong current, these larvae 1s¢ a 
r weeds and shells on the bottom where hie 4 
three examples of stage III were taken were carefully ex@ : 
without success for fixed pearl oyster spat of the same age, ant 
there is no question that those taken were in a free swimm! 
condition, temporary though it may have been. . 
© importance of the above observations on the subjet 
of the dispersal of pearl oyster spat needs no arguing, 4 ap a 
