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DESIGN IN NATURE 



PLATE XCIV 



PLATE XCIV 



Plate xciv. illustrates the anatomy of the amphioxus, once supposed to form a connecting link between the soft- 

 bodied animals and the vertebrates ; also the development of the eye, and the comparative anatomy of the brain. 



Fifi. 1. — Amphioxus (Amphioxus lanceolatus). 



A. Lateral view of Amphioxus lanceolatus. a, Oral cirri ; h, dorsal fin ; • , myomere muscles ; d, metapleural fold ; e, atriopore • 

 /, anal fin ; g, tail. 



B. View of amphioxus from right side, a, Brain ; h, spinal cord ; c, buccal cavity ; d, dorsal fin (skeleton) ; e, dorsal aorta ; 

 /, notochord ; g, dorsal fin ; h, caudal fin ; i, oral cirri ; j, metapleural fold ; h, branchial artery ; I, contractile bulb ; m branchial 

 artery ; n, liver ; 0, portal vein ; p, gonad ; g, atriopore ; r, intestine ; s, anal fin ; t, anus. 



0. a, Nerve cord ; h, notochord ; c, peri-visceral ocelom ; d, gonad ; e, ventral muscles ; /, metapleural cavity ; ij, endostyle • 

 h, ventral blood-vessel ; i, dorsal fin skeleton ; ;', myomeric muscle ; Ic, nephridium ; I, liver ; m, pharynx leading into arterial cavity 

 through clefts ; n, metapleural fold. 



D. a, Right head cavity ; '), left head cavity ; r, collar sac ; d, peri-visceral coelom ; c, myotomes. 



B. Median section of brain of amphioxus. a, Cerebral vesicle ; h, infundibulum ; c, pigment spot ; d, unpaired olfactory lobe • 

 e, ganglion cells ; /, neural tube (after Masterman). ' 



Fig. 2. — Longitudinal section of the eye of embryo of fowl. 



A. From an embryo at about the sixty-fifth hour of incubation. 



B. From an embryo a few hours older. 



C. From an embryo at the fourth day of incubation. The same letters apply to the same parts, a, Corneal lamina ; /), lens in 

 Pig. A, still connected with the corneal lamina and possessing a small cavity (c) in its interior ; d, posterior part of optic 'vesicle • 

 e, folded portion of optic vesicle. ' 



In Figs. B and the lens {g) is detached but still hollow ; e, introverted portion of the primitive optic vesicle, subsequently 

 becoming the retina ; d, posterior part of the optic vesicle, which, according to Remak, probably becomes the choroid coat ciliary 



