NOTES ON BATRAOHIANS OF THE PARAGUAYAN OHACO. 333 



Pig. 5. — Transverse sectiou tlirougli bead of an embryo which was just 

 beginning to be folded off the yolk. Op. ves. Optic vesicle. P/i. Pharynx. 

 mes. Mesoblast. 



Fig. 6. — Section of same series as that sliowu in Fig. 5, through the single 

 branchial pouch {Br.f.) and the ectodermal thickening accompanying it. 



Fig. 7. — Section of same series through auditory region. Aud. Commencing 

 auditory invagination of ectoderm. iV. e^. Notochord. iVewr. cr. Neural crest. 

 P.«. Rudiment of pronephros. 



Fig. 8. — Section of same series through posterior end of archenteron. 

 Red. Rectum. N. en. Neurenteric canal opening into this. hyp. Hypoblast. 

 N.ch. Notochord. 



Fig. 9. — Section of same series further back. N.en, Neurenteric canal. 

 Red. Rectum. 



Fig. 10. — Section of same series showing opening of neurenteric canal (iV. 

 en.) into neural canal ; also anus (Afi.). 



Fig. 11. — Transverse section through anterior end of an embryo, in which 

 the first pair of external gills were beginning to develop. Siom. Cavity of 

 stomodseum. Mnd. Mandibular arch close to its junction with its fellow. 



Fig. 12. — Section of same series passing through tlie rudiment of the eye. 

 Op.lF.an. Anterior layer of optic cup. Op.W.p. Posterior wall of ditto. I. 

 Outer layer of epiblast passing contirmed over mouth of lens invagination. 

 Ph. Pharynx. P.c. Pericardium, mnd. Mandibular arch. 



PLATE 32. 



Fig. 13.— Section of the same series as that shown in Plate 31, Fig. 12. 

 mnd. Mandibular arch. ht. Heart. P.c. Pericardium. 



Fig. 14. — Section from same series through infundibulum {Inf.). P.c. Peri- 

 cardium. S.v, Sinus venosus. 



Fig. 15. — Transverse section through head of slightly older embryo, show- 

 ing later stage in the formation of the lens (/.). 



Fig. 16. — Sagittal section through pineal body {Pin.) of embryo about two 

 days before hatching. Oil. St. Pineal stalk with ciliated lining. Sin. Blood- 

 sinus. 



Fig. 17. — Portion of transverse section of embryo just before hatching, 

 passing through the origin of the first external gill {Ext. Q.). Int. G. Internal 

 gill. 



