178 ACTINOZOA. 



Or, recurring to our diagram, we might look 

 for the appearance of new septa in the chambers 

 5 + 2 and 2 + 5 sooner than in 4 -f 3 and 3+4. 



As might be expected, from abortion and other 

 causes, variations from the above arrangements now 

 and then occur, the careful investigation of which 

 is far from exciting that attention which it so well 

 deserves. 



It is to be remarked that some coralligenous 

 polypes, when in confinement, appear to attain 

 a considerable bulk before any traces of their 

 skeleton can be observed. 



Except in its minute size, and the comparative 

 paucity of its tentacula, the young polype, when 

 first excluded, closely resembles its parent, through 

 whose mouth it usually makes its entrance into 

 the surrounding world. The student will ex- 

 perience little difficulty in obtaining Actinias 

 containing young in several stages of development 

 for detailed anatomical examination. 



It is to be wished that the embryology of the 

 composite Alcyonaria and Zoantharia were more 

 efficiently worked out, since it is just possible 

 that, apart from other modifications of the de- 

 velopmental process, a rudimentary coenosarc may 

 under certain circumstances, be produced before 

 the formation of a distinct polype. 



j 



Ctenophora. The development of the Cteno- 

 phora, while presenting some peculiar features, 

 resembles that of other Actinozoa in the compara- 

 tive rapidity with which its early stages progress, 

 so that the product of the reproductive act, while 

 yet of small size, attains a form and structure 

 similar to the parent. 





