32 Prof. M'Intosh's Notes from the 



coil of a turn and a half, whilst the outer and thicker end 

 does the same. Each ventral muscle, on the other hand, 

 makes a single coil of one turn and a half from its outer 

 end, and thus forms a contrast with the double coil in each 

 dorsal. The small gut lies in the centre, fixed by the 

 ordinary mesenteries. The ventral groove is now open and 

 the ventral hypoderm is considerably thinner. 



Euchone would thus appear to show a more primitive type 

 than Chone, since anteriorly the dorsal and ventral longitu- 

 dinal muscles have a simple loop, after the manner of Nereis, 

 whereas posteriorly the coiled type of muscle has made its 

 appearance. It is also in contrast with Dialy chone of 

 Claparede, in which the coiled muscles begin at the anterior 

 end. 



2. On some Points in the Structure of the Serpulidse, 

 chief y of Pomatocerus triqueter, L. 



Less was accomplished in the minute structure of the 

 Serpulids than in the Sabellids until Claparede took up 

 the subject in his ' Recherches sur la structure des Anne- 

 lides Sedentaires ' *. He dealt in this group for the most 

 part with Protula intestinum, in which he found the hypoderm 

 greatly developed on the ventral surface and richly vascular. 

 In P. infundibutum he noted the pennate arrangement of 

 the longitudinal muscles in section, and pointed out that 

 the intestinal sinus is lodged between the epithelial coat 

 and the circular muscular fibres, and that giant fibres occur 

 in its great nerve-cord and oesophageal commissures. He 

 thought that in Psygmobranchus protensus the distant halves 

 of the ganglionic cord denoted inferiority, especially as in 

 larval annelids this condition is more marked than in the 

 adult. Three pairs of ganglia occur in the thoracic region, 

 the largest being the second, and they are united by trans- 

 verse commissures. He stated that in the Serpulids only a 

 single pair of segmental organs occured, viz., in the thorax, 

 and that they gave exit to the reproductive elements. In 

 his description and figures the voluminous folds of the organ 

 are indicated, and he considered that, by filling up the body- 

 cavity, they conduced to the solidity of the region. 



Schenkf (1874) gave a brief account of the structure of 

 the body-wall in Serpulu uncinata. In his transverse sections 

 he appears to have overlooked the great nerve-trunks, though 

 traces of these occur in his figures. 



* Posthumously published in 1873. 



t Sitzb. K. Akad. Wiss. Wien, Bd. lxx. pp. 1, 2, pi. i. 



