EXPLANATION OF THE LETTERING. 477 



iv.op.g Invagination for optic ganglion. 



Lacunae; lateral plate; labrum. 



.ab.m Longitudinal abdominal muscle. 



ab.n Longitudinal abdominal nerve. 



.a.f Lateral fold. 



ch Lemmatochord. 



c.n Lateral cardiac nerve. 



CO Longitudinal connectives. 



cord Lateral cord. 



e Lateral ethmoids; lateral eye. 



e.n Lateral eye nerve. 



ey Lateral eye. 



ey.g Lateral eye ganglion. 



ey.n Lateral eye nerve. 



f Lateral fold. 



■g Lung. 



g.b. or Lb Lung book. 



.h.tr Longitudinal haemal tract. 



1 Lateral line of canal organs. 



.lo Lateral lobes to the olfactory recess. 



Lch Lateral bands of the lemmatochord. 



Im Lamellae. 



,m.pl Nerve plexus of longitudinal abdominal muscle. 



,n Lateral nerve. 



Ins Lens. 



n.tr Longitudinal neural tract. 



p Lateral process; lateral subdermal process to the mandi- 

 bular plates. 



pi Small bony plates in the fleshy sides of rostrum. 



pLt Lateral plastro-tergal muscle. 



,tr Lateral tracts of brain. 



m Mouth; muscles. 



man Mandibles. 



max Maxillae. 



m.br . Midbrain. 



m.c Merochord; segment of the lemmatochord; marginal cells. 



m.cd.n Median cardiac nerves. 



m.ch. Middle chord; median nerve; notochord. 



m.cl Mesenccele. 



md Mandibles. 



m.d. . . MuUerian duct. 



mes.c Mesocephalon. 



mesen.c Mesencephalon. 



met.c Metacephalon. 



meten.c Metencephalon. 



m.f Median furrow. 



m.l Median line; marginal line of canal organs; mantle layer. 



m.lch Median portion of the lemmatochord. 



m.lo Maxillary lobes. 



m.m Muscle markings. 



m.n Median nerve (mouth). 



