18 li^roL M^lntosWs Notes from t/ic 



nerve-mass l)ulfi;es vciitrally at the sides of the vestibule, and 

 tlie trend ot" the intervening coniniissure is more or less 

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

 central lines of the M l)eing more or less obliterated. 



The eyes (PI. 111. tig. 14) do not appear in the sections 

 until the protective chordoid tissue lias diminished to a 

 small are above the posterior region of the ceplialic ganglia, 

 and when a mei'e 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 

 muscuhir 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 bioun piginent-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 

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

 brownish median region, the dark pigment forming a belt 

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

 found in Psyyinobranchns protensus [^=Protula tubularia, 

 Mont.) and Amphighna mediterranea. 



In Serpula contort uplicat a (= Hydroides norvegica) De 

 Quatrefages describes the cephalic ganglia as large and only 

 sejjarated by a constriction in the middle line, and giving 

 of!" from each side a large branch to the branchite. 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-ivaU. — About the level of the 

 br.iin muscular fibres are fixed to the inner wall of the 

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

 great develojjment, 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 i)ermits this muscle to form a con- 

 tinuous curved sheet, widest below, in the area formerly 

 occui)ied by the skeleton, and it soon approaches its fellow 

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



♦ iMitt. Zool. Stat. Xeapel, Bd. vii. Taf. xxiv. fig. 14. 



