THE ANATOMY OF THil MADBEPORARIA. 9 



"Nesseldriisenstreifen" have precisely the same microscopic 

 appearance as the stomatodseal ectoderm ; while the " Flim- 

 merstreifen/^ 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 

 enormously lengthened cells of M. Durvillei. v. Heider (6), 

 on the same grounds, had previously come to the same con- 

 clusion with regard to Cerianthus. 



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

 surrounded 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 (Octactinise) : 



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 

 development 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 diff'erentiation of mesenteries, which, confined in the 

 Alcyonaria to two, is here extended to six, and more particu- 

 larly 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 can be gathered from this form studied merely by 

 itself; it can only be resolved by a comparative study of allied 

 species. Differentiation of function appears to be incomplete ; 

 both forms are reproductive, both apparently digestive. The 

 most that can be said is that A is, perhaps, more digestive and 

 less reproductive than B, for the filaments are more deve- 

 loped than in the latter form, and I have only once observed 

 an ovum on a modified mesentery. Should the modification 



