1911.] Studies in Heredity. 399 



same age. Such a larva is represented in text-fig. 2. We see that the 

 same number of arms are developed as we found in the larva of Echinoearclium 

 cordatum of the same age. The post-oral arms are, however, longer and the 



Fig. 1. Fig. 2. 



Fig. 1. — Larva of Echinocardium cordatum, Six Days old, viewed from the Dorsal 

 Aspect. 



a.b., aboral spike ; a.l., antero-lateral arm ; b.s., body-rod ; cce., coelom ; I.e., lateral centre 

 of calcification ; p.d., postero-dorsal arm ; p.o., post-oral arm ; p.r., prce-oral arm ; 

 r., recurrent rod. 



Fig. 2. — A Larva of Echinus esculentus, Six Days old, viewed from the Dorsal Surface. 



a.l., antero-lateral arm ; b.s., body-rod ; cce., coelomic sac ; d.a., dorsal arch ; I.e., lateral 

 centre of calcification ; m.p., madreporic pore ; p.d. postero-dorsal arm ; p.o., post-oral 

 arm ; p.r., prce-oral arm ; r., recurrent rod. 



postero-dorsal not so far developed as in Echinoearclium cordatum. The 

 pree-oral arms are indicated merely by slight elevations, but on the dorsal 

 surface of the oesophagus we can see the rudiment of the " dorsal arch," the 

 median centre of calcification, which at a later period of development will 



