THE DIGESTIVR ORGANS OF THE ALOYONARIA. 3839 
disappears, the epithelium of the stomodzum being then 
ciliated and of the same character throughout. Bourne 
regards this as a primitive condition from which the siphono- 
glyph has been derived. In his account of the siphonoglyph 
in Alcyonaria (1883, p. 699) Hickson states that the tendency 
of dimorphic forms is to throw the siphonic function upon the 
siphonizooids, and to eliminate it from the autozooids. 
The siphonoglyphs of the autozooids are not so pronounced 
in the dimorphic Sarcophytum and Lobophytum as in 
Sclerophytum and the zooids of Alecyonium. In Sel. 
hirtum the flagella of the siphonoglyph are fully ‘03 mm. in 
length. In the siphonozooids of well-marked dimorphic 
genera the siphonoglyphs are very large, but are absent in 
the degenerate siphonozooids of Sclerophytum. 
MESENTERIES. 
The mesenteries have the same fundamental structure 
throughout the Aleyonaria. Hickson’s description (1895 and 
1900) of the mesenteries of Alecyonium will apply with 
certain modifications to the zooids of monomorphic, and to 
the autozooids of dimorphic forms. The ventral mesenteries 
of the siphonozooids of the latter are extremely small, and 
even in well-marked cases of dimorphism seldom project 
beyond the lower end of the stomodzum. In some species of 
Sclerophytum they are so minute in the siphonozooids as 
to be almost unrecognisable as such; while in other species 
of this genus they may be entirely absent (Pratt, 1903, p. 
531). 
In the autozooids of Sarcophytum the mesenteries are 
relatively larger than in Lobophytum and Alcyonium. 
In Sclerophytum they are usually smaller and more feebly 
developed. The extreme prominence of the mesenteries in 
Sarcophytum is due to the presence of mesoglceal thicken- 
ings near the free edge, which, when examined with low 
powers of the microscope, have the appearance of enor- 
mous mesenterial filaments. The thickenings, however, are 
