Chap. XX.] STRUCTURE OF THE STVLaSTERID.E. A-g 



Stood. Each colony or coral stock is of a separate sex either 

 male or female. In the female stocks, eggs are developed 

 withm special chambers hollowed out in the calcareous skeleton 

 of the stock, and protected by a wall of hard coral, which often 

 projects on the surfaces of the branches, so that the breeding 

 chambers {ampulhc) show themselves to the naked eye like 

 small warts on the coral twigs. Each egg is developed within 

 the chamber into a cylindrical larva {plaiiula), which is set free 





VKRTICAL SECTION THROUGH THE LIVING TISSUES OF ERRINA 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, gz, cut through, 

 showinfj two of its four tentacles, t, its stomach cavity, f, 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 The gastrozooid is withdrawn within its sac, which lines the gastropore, the 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 

 dactj'lozooid, r/r, 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 ;_ 

 cc ectoderm ; .y spadix ; /' layer of ectoderm covering the planula ; a Layer of 

 soft tissue in the wall of the" ampulla ; ii nemataphore. 



when mature, and swimming off fixes itself and develops a new 

 stock by growing and budding. 



The nurse structures on which the eggs are developed re- 



