SECT. IV 



THE MUSCULATURE 



59 



strictions in the integument. In each segment we 

 find two bands crossing each other diagonally, in 

 addition to those placed between the segments. These 

 strikingly Annelidan dorso-ventral muscle bands of 

 Apus are not, as far as we know, preserved in any 

 of the higher Crustacea, being rendered useless by 

 the development of the exoskeleton. Clear traces of 



Fig. 14. — Transverse section through Apus cancnformis, to show the distribution of 

 the musculature, h, heart ; dm, dorsal ; vin, ventral muscle bands ; cm, circu- 

 lar musculature (as shown in Fig. 15, A~); civ, dorso-ventral musculature {cf. 

 Fig. II, tni); m, membrane enclosing the intestinal and genital sinus ; i, intes- 

 tine ; g, genital glands ; e, eggs ; a and b have reference to Fig. 15. 



them are, however, found in Limulus, where their 

 points of attachment have drawn in the outer integu- 

 ment to form the entapophyses. Their use in Apus 

 will be discussed in the sections on circulation 

 and reproduction. They are not developed in the 

 posterior rudimentary segments. 



The muscles of the limbs present complications 



