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been prevented by the gill apparatus (see Part I), apparently consist 
of 17 segments (see fig. 25 dorsal aspect), the first segment (/IT) 
being situated in front of the eye and the seventeenth (V) in front 
of the last gill cleft. The strip of muscle labelled U.I.M. is attached 
below to the subocular arch and possibly represents the more ventral 
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Fig. 18 (x cire.1). Side view of the head region of Geotria australis after 
removal of the lateral skin. 
Fig. 19 (x cire.1). Ventral view after removal of ventral skin. 
Fig. 20 (x circ. 1). Lateral view after removal of some of the dorsal and all 
of the sub-branchial myotomes and of the middle portion of X VJ. 
portion of the third dorsal myotome. The muscle marked #.Y.M. is 
a myotome-like muscle attached to the posterior outer side of the 
eye-ball. The sub-branchial musculature (a secondarily segmented 
