(73) 



STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 513 



are two prominent anal lobes (fig. 5, an. I.), which are impor- 

 tant agents in locomotion. 



The cuticular integument is thin and rather transparent, so 

 that in the younger larvae many of the internal organs can be 

 seen through it. In older larvae the fat-body assumes large 

 proportions and gives the larva a creamy appearance, obscur- 

 ing the internal organs. The cuticle (fig. 14) is composed of 

 an outer rather thin layer of chitin (ct.), which is continuous 

 with the chitinous intima of the tracheae, and also with the 

 chitinous lining of the stomodyeal and proctodaeal regions of 

 the alimentary tract. Below this layer there is a thicker 

 layer of chitin (ct.') f which does not stain so deeply. In 

 places this lower layer is penetrated by the insertions of the 

 muscles. The cuticle lies on a layer of stellate hypodermal 

 cells (h*y.) } which are well innervated, and attain a large size 

 in the posterior segments of the body. 



2. MUSCULAR SYSTEM. 



The muscular system of the larva (PI. 31, fig. 16) consists of 

 a segmental series of regularly repeated cutaneous muscles, 

 forming an almost continuous sheath beneath the skin, 

 together with a set of muscles in the anterior segments of 

 the body which control the cephalo-pharyngeal sclerites and 

 pharynx. In addition to this there are a set of cardiac 

 muscles and the muscles of the alimentary tract. 



I have been unable to find a detailed description of the 

 muscular system of the muscid larva, and I do not think that 

 Lowne's excuse for dismissing the cutaneous muscles of the 

 blow-fly larva with a very brief statement, because " the 

 details possess little or no interest," was justified, considering 

 how little is known about the muscular systems of insect 

 larvae, and constant reference to the classic work of Lyonet 

 (1762) on the caterpillar is not sufficient to satisfy the 

 inquiring student of to-day. The muscular system of the 

 larva, therefore, will be described in some detail. 



Muscles of the body-wall. The cutaneous muscles 



