GLOSSARY 415 



Roe. The ova or spawn of fishes and amphibians, especially when still 

 inclosed in the ovarian membranes. 



Rudimentary. In an early stage of development. 



Sarcode. The gelatinous material forming the bodies of sponges and other 

 low animal forms. 



Somites. The segments of which an articulated body is composed. 



Stomodeum. The primitive mouth and esophagus found in actinozoans 

 and in the embryos of annelids and arthropods. 



Symbiosis. The living together of two species of animals or plants, inti- 

 mately and permanently, to their mutual advantage. 



Syndactylous. Having the toes united for some distance, but without a 

 web. 



Trochosphere. That larval form of various worms, mollusks, and mol- 

 luscoids which has a circlet of cilia. 



Vestige. A structure of the past left behind; a degenerate organ or struc- 

 ture. 



