TAHITI. 



529 



produce free-swimming Medusae. In that of the Stylasteridce on 

 the other hand, the process is well understood. Each colony 



VERTICAL SECTION THROUGH THE LIVING TISSUES OF ERKINA LABIATA GREATLY MAGNIFIED, AND 

 WITH ALL THE CALCAREOUS SKELETON EXCEPT THE STYLE REMOVED. 



The mass is seen to be made up of a network of canals, which canals are shown in many places cut 

 across. On the left is a gastrozooid, c 2, cut through, showing two of its four tentacles, t, its 

 stomach cavity, c, and its style, s t. Large canals pass from the stomach cavity to join the 

 general canal network. The gastrozooid is withdrawn within its sac, which lines the 

 gastropore, the wall of which is removed. To the right of the gastrozooid is seen a single 

 dactylozooid, d 2, partly protruded from its sac. On the extreme right is seen an embryo or 

 planula doubled up within the ampullar sac and cut through. The planula is mature and 

 nearly ready for escape ; e Endoderm of the planula ; e c ectoderm ; s spadix ; b layer of 

 ectoderm covering the planula ; a layer of soft tissue in the wall of the ampulla ; 

 n nemataphore. 



or coral stock is of a separate sex, either male or female. In 

 the female stocks, eggs are developed within special chambers 

 hollowed out in the calcareous skeleton of the stock, and pro- 

 tected by a wall of hard coral, which often projects on the 

 surfaces of the branches, so that the breeding chambers (am- 

 pulla) show themselves to the naked eye like small warts on 

 the coral twigs. Each egg is developed within the chamber into 

 a cylindrical larva (planula), which is set free when mature, and 

 swimming off fixes itself and develops from itself by growing 

 and budding a new stock. 



The nurse structures on which the eggs are developed, repre- 



M M 



