218 THE VOYAGE OF H.M.S. CHALLENGES. 



entoderm of the mesenteries, excepting in the case of Cirripathes propinqua, where a 

 single fiat row of delicate fibres is present on each side of the primary mesenteries. 

 This portion of the entodermal muscular system is, however, too rudimentary to admit of 

 a distinction being made according to the direction of the fibres. The comparative 

 development of the ectodermal as compared with the entodermal muscular fibres appears 

 to indicate that the latter are of later origin. The mesenterial filaments are apparently 

 outgrowths from the lower margin of the transverse mesenteries, and bear a cap of 

 ectodermal cells at their free extremities. The reproductive organs are developed in 

 connection with the transverse mesenteries only. The germinal cells are derived from 

 the entoderm and may undergo differentiation within that layer, or may be enclosed in a 

 mesogloeal capsule. 



The Antipathinae approach the Cerianthidas more closely than the Hexactiniaj in 

 structure, particularly in the following points : — 



1. The arrangement of the mesenteries. 



2. The relatively thin mesoglcea, which is entirely devoid of stellate connective-tissue 

 cells. 



3. The presence of an ectodermal muscular layer in the stomodaeum and body-wall. 



4. The rudimentary condition of the musculature of the mesenteries. 



