WERNER MARCHAND 21 



The structure of the chitinous membrane has been studied in de- 

 tail by Lecaillon in Tahanus quatuornotatus Meig. The membrane 

 consists of three layers or zones, the innermost soft and of greatest 

 thickness, the two outer ones hard and elastic; of the latter the inner 

 (median) is much thicker than the external one. By staining methods 

 the three layers can be differentiated. The fine striation of the 

 cuticle is formed by the median layer, which is thickened in the form 

 of narrow longitudinal ridges. The hairs are formed exclusively of 

 the external layer. The muscles to the integument are attached to 

 the median zone. 



The muscular system is strongly developed, consisting of the re- 

 tractor and extensor muscles of the head, and probably similar muscles 

 governing the retraction and extension of the syphon; also of muscle 

 fibers arranged more or less vertically to the integument, and circular 

 muscles which function in the contraction of the circular segmental 

 ridges and the retraction and exsertion of the parapodia. The mus- 

 cular system is partly illustrated but not described by Graber (1882) 

 (Plate 8, Fig. 100, a). Lecaillon (1906) notes the muscular inser- 

 tions in the integument, stating that the muscles pass through the 

 inner chitinous layer, losing here their transverse striation, and being 

 inserted in the median layer. Various muscles go to the organ of 

 Graber, described later, by means of which this organ is displaced in 

 various directions. (Plate 9, Figs. 104 to 106, and Plate 10, Figs. 

 112, 115, and 116.) 



Alimentary Canal (Plate 7, Fig. 98). — This has been studied by 

 Patton and Cragg in Tahanus alhimedius (also in other species?). It 

 is much shorter and less complicated than that of the larva of 

 Stomoxys calcitrans, described by the same authors. The esophagus 

 opens into a short, cylindric proventriculus, which is also a highly 

 muscular structure, and is sharply distinguished from the succeeding 

 part of the gut by its clear translucent appearance in the fresh con- 

 dition. The mid gut extends from the proventriculus to the hind 

 end of the body, and is thrown into one or two simple coils, not con- 

 stant in their position. It is separated from the proventriculus by a 

 short constriction, and is again constricted at the posterior end, just 

 anterior to the opening of the Malpighian tubes. Between these 

 points the lumen is wide and is thrown into numerous sacculations 



