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ends. The branchial sac is pierced by two oblique bands of stig- 
mata (Fig. 23 sg). The life history is very complicated. The egg 
develops into a tailed larva, which develops into a " nurse " ; the 
latter is asexual, and produces three kinds of buds on a stolon, viz. 
(1) nutritive buds which provide the " nurse " with food, (2) foster 
forms which are set free as cask-shaped bodies with eight broad 
muscle-bands, and (3) sexual forms which are attached for a time 
to the foster forms, but which later become free and give rise 
to the egg. 
Order III. — Lakvacea. 
The Larvacea are very minute Tunicata which live at the surface 
and swim by means of a tail-like appendage, resembling in this and 
Fig. 24. 
Oikopleura cophocerca in its '* house " (after Fol) ; seen from right side, x 6. 
Arrows indicate course of the water ; x, lateral reticulated parts of the " house." 
certain other respects the tadpole larva of other Tunicata. They 
are able to form a temporary test or " house " many times larger 
than the body (Fig. 24). The organism itself, which is almost lost 
