Journal of conchology . is easy to mistake them forrotifers—especially if the zone of cilia happens to be in active motionduring examination. Dr. Korschelt, in the course of his remarks, says:—The chiei 8s JOURNAL OF CONCHOLOGY, VOL. II, NO. 3, JULY, 1904. features in the larval organization are recognizable from fig. i,—thebivalve shell (figs. 2—3, s.), the velum with its retractors, and aciliation, also found in the larvae of other mussels, in the neighbour-hood of the anus. As in the Trochophora, the oral opening liesbehind the powerful zone of cilia on tlie velum. In older larvae thereappe
Journal of conchology . is easy to mistake them forrotifers—especially if the zone of cilia happens to be in active motionduring examination. Dr. Korschelt, in the course of his remarks, says:—The chiei 8s JOURNAL OF CONCHOLOGY, VOL. II, NO. 3, JULY, 1904. features in the larval organization are recognizable from fig. i,—thebivalve shell (figs. 2—3, s.), the velum with its retractors, and aciliation, also found in the larvae of other mussels, in the neighbour-hood of the anus. As in the Trochophora, the oral opening liesbehind the powerful zone of cilia on tlie velum. In older larvae thereappears behind the mouth a peculiar pigmentation, which often has abilobed appearance (figs. 2-4, //.), which I was at first inclined toregard as the earliest indication of the byssus-gland; the position ofthe latter, however, would not well agree with this. A closer investiga-tion of the subsequent stages will be necessary before we can decidewhether a more important significance attaches to this formation. IlS. Fig. 1.—Older larva o( Dreissensia, with expanded velum (vei.), which in the figure is viewedobliquely ; /, pigmentation of the velum : //, pigmentation in the vicmity of the mouth ;s, the valves of the shell (from Korschelt, 92). The larvae may be looked for at the end of June and early part ofJuly. They swim about for eight days or so, feeding apparently uponminute floating algte; during this pelagic existence the foot makes itsappearance, and shortly after the larva sinks to the bottom for velum then gradually disappears; the mantle and gills develop;the foot attains larger dimensions, and is capable of being protrudeda long way from the shell, and the young mussel now progresses solelyby the aid of this vermiform organ, which, when stretched out, goesthrough the movements of a feeler, and fixing itself by its extremity,contracts and so drags the body after it. The foot has now becomean organ of locomotion in place of the lost velum, and by its ai
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