THE ANTHOZOA 



turned away from it. There are also three edges in each pinna a basal, 

 attached to the rachis ; a lower, destitute of zooids ; and an upper, more 

 or less convex, bearing zooids. The axis of the Pennatulacea, when 

 present, is entirely enclosed within the tissues and is surrounded by an 

 epithelium. There is not sufficient evidence to show from what layer 

 this epithelium is derived, but the evidence, as far as it goes, points to 

 its being of endodermic origin. The development of Renilla has been 



FIG. XVII. 



1. A young colony of Pennatula phosphorea 

 seen from the right side. P, the calyx of the 

 mother zooid ; Z, the first siphonozooid ; pi, the 

 first lateral autozooid formed as a bud from P ; 

 j>3, the third lateral autozooid. 



2. A somewhat older colony seen from the 

 asulcar aspect, z*, z 2 , lateral siphonozooids 

 formed at the bases of p 1 , p 2 , the first and 

 second lateral autozooids ; p*-p7, successively 

 formed lateral autozooids. 



3. Diagrammatic section through the ter- 

 minal autozooid and siphonozooid of a young 

 colony of Pennatula phosphorea. S, sulcar inter- 

 mesenterial chamber ; As, asulcar chamber ; st, 

 stomodaeum of siphonozooid. 



4. A section of the same colony through 

 the autozooid, in 2. S, sulcar chamber of the 

 axial zooid ; As, asulcar chamber ; the two are 

 separated by the transverse partition, in which 

 two lateral canals (stem canals)are being formed ; 

 p 1 , p u , lateral autozooids. 



5. A section somewhat lower down. The 

 axis X is bem.* formed in the partition between 

 the two lateral chambers ; Z, a siphonozooid. 

 (All the figures after Jungersen.) 



thoroughly studied by E. B. Wilson (96), whose memoir should be 

 consulted by the reader ; but Renilla has no axis, and Jungersen was 

 unable to obtain stages of Pennatula phosphorea young enough to throw 

 light upon the question. The growth of the peduncular septum in 

 Renilla has been fully described by Wilson, and the same mode of 

 development apparently holds good for Pennatula. It arises as a double 

 fold of endoderm containing a delicate lamina of mesogloea at the basal 

 end of a larva of forty hours. This fold grows rapidly upwards and 

 becomes continuous with the asulcar mesenteries at the point where 

 these unite, as they do in Renilla, with the asulco-lateral pair. Thus 

 the coelenteron of the mother zooid is early divided into two cavities by 

 a transverse partition which separates the asulcar portion of the coelenteron 

 from the sulcar portion containing the mesenteries. The lower or 

 proximal portion of the mother zooid becomes, in course of growth, 



