324 
PROF. E. W. MAOBRIPE. 
PLATE 15. 
[All the following figures represent larvse developing from the eggs 
of Echinocardium cor datum which have been fertilised with the 
sperm of Echinus esculentus.] 
Fig. 12. — Hybrid blastula twenty-four hours old. mes. Primary 
mesenchyme. 
Fig. 13. — Hybrid gastrula two days old. cil. Anterior tuft of 
cilia^ 
Fig. 14. — Hybrid gastrula (from another culture) two days old. 
cos. Rudiment of coelom, calc. Rudiment of skeleton, wies. Secondary 
mesenchyme. 
Fig. 15. — Hybrid larva four days old viewed from the dorsal side. 
a. 1. Antero-lateral rod of skeleton, h. r. Body-rod. cil. Anterior tuft 
of cilia now incorporated with longitudinal ciliated band. oes. Larval 
oesophagus not yet joined to stomodseum. r.r. Vestigial recurrent 
rod. 
Fig. 16. — Hybrid larva four days old, more advanced in development 
than that shown in fig. 15 ; viewed from the dorsal side. 
Fig. 17.^ — Hybrid larva five days old viewed from the dorsal surface. 
c.r. In-bent crook at aboral end of body-rod. 
Fig. 18. — Hybrid larva five days old viewed from the left side. ad. 
Ridge of thickened epithelium in the oesophagus carrying the aboral 
ciliated band. an. anus. li. r. Horizontal branch of the skeleton. 
Fig. 19. — Hybrid larva six days old viewed from the dorsal suiface. 
r. r. Recurrent rod. 
Fig. 20. — Hybrid larva seven days old viewed from the dorsal surface. 
Notice that one antero-lateral arm has been absorbed. 
Fig. 21. — Hybrid larva eight days old viewed from the dorsal surface. 
mad., mad.' The two madreporic pores. 
Fig. 22. — Hybrid larva eight days old viewed from the ventral surface. 
an. Anus. h. r. Horizontal branch of larval skeleton. 
Fig. 23. — Hybrid larva eight days old viewed from the left side. 
This is the only hybrid in which the aboral sj)ike and its skeleton have 
been developed. Notice the distortion of the larva. It is as if the left 
antero-lateral arm and the left side of the oral lobe liad been forcibly 
twisted away from the spectator, b. r. The right and left body-rods 
crossing each other, cil. Posterior tuft of cilia. 
