146 



DEVELOPMENTAL CHANGES IN THE EARLY EMBRYO 



Craniol nerve V 



Notochord 

 Anterior cardinal vein 



Olfactory pit 



Diocoel 



Pigmented layer 

 Retina 

 Lens 



- Cranial nerve V 

 Cranial nerve VII 

 Otic vesicle 



Cranial nerve IX 

 Cranial nerve X 

 Lateral line nerve 



^ — Somite 

 Neurocoel 



Spinal nerve 



The 7 mm. frog tadpole: frontal section. 



(epimere), an intermediate cell mass (mesomere), and a lateral plate 

 (hypomere). 



The epimere (segmental or vertebral plates) posterior to the phar- 

 ynx becomes divided into sections known as the metameric somites. 

 These are developed in sequence from the anterior to the posterior so 

 that at any time in the development of an early embryo the anterior 



