8 G. HERBERT FOWLER. 



ordinary endoderm, and their appearance suggests strongly that 

 their condition is merely an exaggeration of that of the " Flimmer- 

 streifen " of the brothers Her twig, i.e., of the two lateral lobes of the 

 mesenterial filament. 



In a recent paper (5) Dr. Wilson has suggested that these lateral 

 lobes are ectodermic in origin, circulatory in function, and homo- 

 logous with the "ectodermic bands " described by him on the axial. 

 mesenteries of certain Alcyonaria. I may here state that, so far as 

 histological evidence from the adult is valuable, it points, in all the 

 Madreporaria that I have yet examined, distinctly in the other 

 direction. The central " Nesseldriisenstreifen " have precisely the 

 same microscopic appearance as the stomatodseal ectoderm ; while 

 the " Flimmerstreifen," in the unbroken gradation by which they 

 pass into the endoderm, and by their characteristic staining, seem 

 to be much more nearly connected with that layer than with the 

 ectoderm, and to exhibit an intermediate condition between the 

 ordinary cubical or pavement cells of the endoderm and the enor- 

 mously lengthened cells of M. Dunillei. Von Heider (6), on the 

 same grounds, had previously come to the same conclusion with 

 regard to Cerianthus. 



The ova, which in my specimens were few in number, are sur- 

 rounded by a mesodermal capsule, and possess the ordinary structure. 

 In the one case, in which an ovum was observed on a modified 

 mesentery, it was borne on the neck between the endodermic swelling 

 and the mesenterial filament. 



d. General Conclusions. — This form has four interesting 

 features in common with the Alcyonaria (Octactiniae) : — 



1. The marked tendency to an absence of polyps on one (the 

 ventral) side of the branch and branchlets. 



2. The very definite orientation of the polyps by a stronger develop- 

 ment of axial and abaxial septa ; and the concomitant bilateral 

 symmetry, the plane of bisection being at right angles to the long 

 axis of the branch or branchlet. 



3. The differentiation of mesenteries, which, confined in the 

 Alcyonaria to two, is here extended to six, and more particularly 

 to two of these, though not the same two as in the other group. 



4. The distinct dimorphism. 



Of the true significance of this dimorphism no certain explanation 



