ASYMMETRICAL DUPLICITY IN THE CHICK. 



109 



EXPLANATION OF THE PLATES. 



Kefeeence Letters. 



Lat.l.std. 



L.aud.ves. 



L.Bt.T. 



L.Hy.P. 



JL.lat.aor.sp. 



PI. L 



= lateral limiting sulcus. 

 = left auditory vesicle. 

 = left heart-tube. 

 =left hyoid pouch. 

 =left lateral aortic space. 



Som. 



Som.mes. 



Sp. 



Sp.mes. 



Tel. 



=-left optic evaginatiou. 



= mesencephalon. 



= mesoblastic somites. 



=omphalomesenteric vein. 



=oral plate. 



= pleuro - pericardial 



cavity. 

 =" primitive groove." 

 = right auditory vesicle. 

 = right heart-tube. 

 = right hyoid pouch. 

 =right lateral aortic 



space. 

 = right mesodermal (?) 



proliferation. 



= Rudiments u & (3. 



=somatopleure. 



= somatic mesoderm. 



= splanchnopleure. 



= splanchnic mesoderm. 



—Telencephalon. 



fig. 1. Photograph of the Blastoderm, stained virith Borax carmine and 

 mounted in balsam. 



PI. II. fig. 2. Transverse section of the primitive streak-like Rudiment /3. 



PI. I. fig. 3. Semi-diagrammatic representation of the anterior (cephalic) region of 

 embryonal formation a. 



Pis. II., III. tigs. 4 & 5. Transverse sections of the anterior (cephalic) region of 

 embryonal formation a. 

 E 1. In the plane of the telencephalon. 



E 2. Posterior to E 1 in the region of the anterior extension of the fore-gut. 

 E 3. In thp anterior region of the diencephalon. 

 E 4. Through the diencephalon, showing the left optic evagination, and the 



infundibular depi-ession. 

 E 5. Ik the region of the mid-brain, showing the dorsal aortse and the 



heart-tubes. 

 E 6. Posterior to E 5. 

 E 7. In the region of the hind-brain. 



E 8. Through the plane of the auditory vesicles and the anterior intestinal 

 portal. (See also text-fig. 1, p. 87.) 

 PI. I. fig. 7. A. Diagrammatic representation of a median longitudinal section of 

 the anterior region of a normal chick embryo of 13 somites (after Lillie, 

 " The Chick," fig. 67). For comparison with B. 

 B. Diagrammatic reconstruction of the median longitudinal section of the 

 embryonal formation a. For comparison with A. 



