452 PROCEEDINGS OF THE ACADEMY OF [1894. 



embedded in the base of the organ on each side. On tlie IVth 

 and Vth somites the appendages are less highly developed, but are 

 similar, the low dorsal ridges bearing on each side a pair of slender 

 and simple cylindrical processes. 



An examination of figures lb, Ic, and Id will make the structure 

 of the characteristic dorsal appendages clear. The transverse dorsal 

 ridges are built up chiefly of short, thick, longitudinal muscle fibres, 

 which extend between the anterior and the posterior covering of 

 hypodermis. Spaces partly filled with a connective tissue network 

 are observable among the fibres, and a similar more extensive space 

 (a, figs. 16, Ic), separates the muscles of the dorsal organ from the 

 longitudinal muscles of the body walls. A few vertical muscle fibres 

 are also developed in the lateral margins of the ridges. Over this 

 firm muscular basis the hypodermis, with the circular muscle layer, 

 extends, and this alone, with a core of loose, spongy tissue, probably 

 derived from the subderiiial connective tissue, forms the terminal 

 processes and lobes, (fig. Id.) In the formation of these dorsal 

 appendages, from the body walls, it would seem that the loose fold of 

 hypodermis and circular muscle fibres that rises freely from the longi- 

 tudinal muscle fibres is pinched up, as it were, at several points, from 

 which the skin and connective tissue underlying it proliferate to 

 form the marginal processes, while the space remaining becomes filled, 

 save for a few narrow clefts, with muscle fibres that proliferate from 

 the ends of the longitudinal muscle fibres of the body walls at the 

 points where these meet the hypodermis. 



The alimentary canal is enlarged to form a saccular stomach in 

 the four anterior body somites, while posteriorly it is narrow and 

 tubular, and, with the exception of a slight transverse loop in the 

 Vllth and Vlllth somites, proceeds directly to the anus on the dor- 

 sum of somite X. 



The jaws are small, measuring .02 mm. in breadth. They are of 

 similar form, being quadrideutate, with a median pair of long, 

 sharply-conical, widely- separated, and divergent teeth, bent at a 

 nearly right angle from the plane of the somewhat quadrangular 

 basal plate. In extreme lateral positions are a pair of inconspicuous 

 blunt teeth. When in position the basal plates are fixed in the 

 cuticle of the pharynx, and the points of the teeth of the two jaws 

 cross in the pharyngeal lumen. 



The spermatheca lies in tlie Vth somite to the left of the intestine. 



