BIOCHEMICAL ARCHITECTURE 15 



all point rather towards an affinity with vertebrate elastin, in 

 distinct contrast to the collagen-like ectodermal cuticle. The 

 earthworm elastin differs from elastin originating in vertebrates in 

 that it is not birefringent or auto-fluorescent. Hydrolysis leads to 

 the appearance of only four identified amino-acids, proHne, 

 hydroxyproline, valine and glycine. Van Gansen (1960) suggests 

 that the lining of the gizzard is an elastin secreted from the cells of 

 the organ in a manner comparable to the secreted collagen of the 

 epidermal cuticle. 



Chaetae 



Closely associated with the cuticle and an integral part of the 

 surface presented by the earthworm to the outside world, are the 

 chaetae. There are usually four pairs of these small hard structures 

 in each segment and they are secreted by glands in the dermal 

 layers of the skin. They are used in locomotion as the animal passes 

 along its burrow, and serve as an efficient anchor to maintain 

 contact with the burrow when the anterior end is extended on the 

 surface of the ground. 



Chaetae can be isolated from the body by digestion with hot 

 dilute alkali and when oriented parallel to one another show X-ray 

 diffraction patterns very like those of j8-chitin from vertebrates. 

 The two substances are not identical but the similarities are greater 

 than are the similarities between earthworm cuticle and vertebrate 

 a-chitin. Annelid chitin differs in small ways from typical arthropod 

 chitin (Rudall, 1955). The chitin is associated with protein in the 

 cuticle. 



The chaetae of A. longa are amber in colour and Dennell (1949) 

 suggests that this colour is due to tanning by an orthoquinone, as is 

 the case with the browning of insect cuticle. Dennell (1949) also 

 states that the chaetae dissolve at the proximal end in boiling 

 concentrated KOH, followed by cold concentrated HCl, to leave a 

 thin sheath or covering cap. This sheath covers precisely that part 

 of the chaetae which is extended in locomotion and its resistance to 

 HCl suggests a resemblance to the thin epicuticle of an insect. 



Phosphagen 



The energy cycles of animals are continually metabolizing and 

 synthesizing high energy phosphate bonds which are mobilized 



