MINUTE ANATOMY OF MEDITERRANEAN NEMERTEANS, 25] 
penetrate at random into the body cavity, but mutually com- 
bine, giving rise to fibrous dissepiments (Pl. XIII, fig. 8) placed 
at regular intervals—one between each intestinal coeeum— 
and serving to attach and carry the intestine (g) and the 
small anastomotic blood-vessels (e). Moreover these vertical 
interceecal septa are again composed of two separate layers 
lying close against each other in the normal condition and 
separating when the sexual organs begin to develop. 
Eggs and spermsacs (f) take their origin between these 
layers. The fibrous septa might be regarded, on account of 
all these peculiar functions, as a kind of primitive mesentery. 
Cavity of the Proboscidian Sheath. 
Mr. MacIntosh was the first to recognise this cavity with 
its proper muscular wall and its characteristic corpusculated 
fluid as entirely separated from the general body-cavity with 
which it had been confounded by Keferstein and Quatrefages. 
This cavity, extending through the entire length of the 
animal, was present in all the species which came under my 
notice. The muscular wall, ordinarily attached to the dorsal 
side of the body-cavity, was exceedingly thick in Drepano- 
phorus (n. gen.), being chiefly composed of circular fibres 
intermixed with longitudinal bundles. The inside was lined 
with elongated papille. ‘This stronger development of the 
walls no doubt stands in connection with the great facility 
with which these species extrude their proboscides. 
Proboscis. 
The minute structure of this organ as described by Mr. 
MacIntosh could be verified in numerous specimens. In 
transverse sections of the proboscis of Meckelia somatotomus 
(Leuck.), the curious deviation of fibres from the internal 
and external circular muscular layers presented a somewhat 
different aspect, the mutual interchange of fibres not taking 
place on one side only, but on two diametrically opposed 
points. 
With respect to the anatomical structure of the armed 
proboscis, my conclusions, are chiefly based upon the different 
species of Drepanophorus (n. g.)! 
Mr. MacIntosh distinguishes six different layers in the 
anterior part of the enoplan proboscis, and for the first time 
mentions the presence of a separate layer with rather a puz- 
zling character (his reticulated or beaded layer), enclosed 
‘1 For more details about this genus, vide Niederl., ‘Archiv fiir 
Zodlogie,’ Bd. II, Heft 2. 
