444 



JAS. P. HILL. 



Nervous 

 system 



Eye 



Ear 



Nose 



Mouth 



P. nasuta, Stage C. 



7 mm. 

 from crown to rump. 



P. obesula, Stage D. 



8-75 mm. 

 from crown to rump. 



Distinct hemispliere 

 anlagen. Dorsal and 

 ventral spinal nerve- 

 roots united. Spinal 

 cord reaches tip of 

 tail, but is here ru 

 dinientary. Ante 

 rior commissure of 

 spinal cord distinct. 

 Anterior and poste 

 rior white columns 

 laid down. Lateral 

 columns very thin. 

 Hypophysis still 

 connected with roof 

 of mouth by a stalk 

 with a narrow lu- 

 men. 



Optic stalk still open. 

 No pigment inouter 

 wall of optic cup. 

 Lens with cavity 

 Mesoderm has pen. 

 etrated into optic 

 cup. 



Auditory vesicle sur 

 rounded by con- 

 densed mesenchyme 

 Long ductus endo- 

 lymphaticus. Eva- 

 ginations for semi- 

 circular canals. 



Slit-like nasal sac in 

 open communica 

 tion with mouth. 



Palate unformed. 



Mesial hemisphere 

 wall tliickened in 

 hippocampal region 

 but still no fissura 

 arcuata. Hypophy- 

 sis no longer com- 

 municates with the 

 oral cavity. 

 Indications of 



"Sprossen." 



P. nasuta, new-born. 



Stage E. 



14 mm. crown to rump. 



Head length 6 mm. 



Optic stalk still with a 

 lumen. Outer wall 

 of optic cup pig 

 mented. Ovalish 

 lens cavity. No 

 differentiation of 

 the retina into 

 layers. 



Anterior vertical semi- 

 circular canal now 

 formed. Utriculus 

 and sacculus still in 

 wide communica- 

 tion. Periotic cap- 

 sule condensed me- 

 senchyme. 



Nasal cavities still 

 open directly into 

 mouth. Shallow- 

 grooved anlagen of 

 the organs of Jacob 

 son. Solid anlagen 

 of lachrymal ducts. 



Palate unclosed. Lens- 

 shaped Zahnleisten 

 anteriorly. Taste- 

 buds differentiating 

 on tongue. 



Marked fissura arcuata 

 along mesial hemi- 

 sphere wall. Cor- 

 pora striata deve- 

 loping. Hypophy- 

 sis dorso-ventrally 

 compressed. 

 " Sprossen " not 

 very marked. 



Retina deeply pig- 

 mented, no differen- 

 tiation into layers. 

 Eyelids united and 

 covered by epitri- 

 chium. 



Semicircular canals 

 formed, but peri- 

 lymphatic spaces 

 not yet differentia- 

 ted. Cartilaginous 

 periotic. 



Adult form nearly es- 

 tablished.' Turbinal 

 projections arising. 

 Jacobson's organ 

 formed, and its car- 

 tilage laid down. 

 Lachrymal duct 

 opens into nose. 



Palate formed, and 

 invests larynx pos- 

 teriorly. Teeth 

 anlagen. Tongue 

 grooved, and with 

 distinct taste-buds. 



