18 Prof. M'Intosh's Notes from the 



nerve-mass bulges ventrally at the sides of the vestibule, and 

 the trend of the intervening commissure is more or less 

 straight — from the change in the roof of the vestibule, the 

 central lines of the M being more or less obliterated. 



The eyes (PI. III. fig. 14) do not appear in the sections 

 until the protective chordoid tissue lias diminished to a 

 small arc above the posterior region of the cephalic ganglia, 

 and when a mere chink above the gullet indicates the external 

 pit in communication with the sea-water. The oesophagus 

 itself is now enclosed in connective tissue and circular 

 muscular fibres. The eyes rest on the ganglia, and the great 

 trunks arise near, and show a pale faintly granular central 

 area and a thick investment of neuroglial cells. The eyes 

 have dense brown pigment-cells apparently radially arranged 

 round a pale region, which probably represents a lens, a 

 thinner layer of the pigment occurring on one side of the 

 elliptical organ according to the level of the section. In 

 some sections a pale spot appears in the centre of the pale 

 brownish median region, the dark pigment forming a belt 

 exteriorly. These eyes appear to be similar to those Meyer * 

 found in Psygmobranchus protensus ( = Protula tubularia, 

 Mont.) and Amphiglena mediterranea. 



In Serpula contortuplicata (= Hydroides norvegicci) De 

 Quatrefages describes the cephalic ganglia as large and only 

 separated by a constriction in the middle line, and giving 

 off from each side a large branch to the branchiae. The 

 oesophageal connectives are longer than in Sabella, and from 

 the first widely separated pair of ganglia a considerable 

 trunk passes to the " voile palleal " (the thoracic membrane). 

 The ventral cords remain separate, and ganglia connected 

 by a slender commissure occur in every segment. The 

 trunks are wider apart anteriorly than posteriorly. 



Muscular System and Body -wall. — About the level of the 

 brain muscular fibres are fixed to the inner wall of the 

 chordoid skeleton (PI. II. fig. 10, m.), which here attains 

 great development, and their general trend shows that they 

 draw the horseshoe bend of the skeleton close. Proceeding- 

 backward, a strong longitudinal muscle (PI. I. fig. 1, m.) 

 appears at the ventral end of the diminished chordoid area, 

 and a smaller muscle above the skeleton, and the disappear- 

 ance of the skeleton permits this muscle to form a con- 

 tinuous curved sheet, widest below, in the area formerly 

 occupied by the skeleton, and it soon approaches its fellow 

 of the opposite side, separated only by a series of transverse 



* Mitt. Zool. Stat. Neapel, Bel. vii. Taf. xxiv. fig. 14. 



