84 



the most persistent or most strenuous action are richest in 

 sarcoplasm." 



In Cancer the muscles present all grades of colour, 

 from an opaque yellowish brown (muscles of scapho- 

 gnathite) to a transparent white (muscles of appendages). 

 Undoubtedly, the most active muscles of the body are 

 those of the scaphognathite, and probably the flexors and 

 extensors of the abdomen are the most sluggish (in the 

 Macrura the abdominal muscles are very strenuous). I 

 append a list of muscles, commencing with the most 

 strenuous and darkest in colour and finishing with the 

 least active. In all cases the position of a muscle on the 

 list for colour agrees with its position regarding its 

 activity. 



1. Muscles of the scaphognathite. 



2. Muscles of the heart. 



3. Mandibular muscles. 



4. Anterior cardiac muscles. 



5. Extensor muscles of flagella of maxillipedes. 



6. Gastric muscles (other than the anterior cardiacs). 



7. Muscles of the appendages. 



8. Extensor and flexor muscles of the abdomen. 



COELOM AND BODY CAVITY. 



Arthropods in general are characterised by the 

 presence of a greatly reduced coelom in the adult. This 

 reduction of the coelom is the result of the increase in the 

 blood-holding spaces or sinuses. This system of swollen 

 sinuses, which contain the venous blood, has produced a 

 series of cavities lying between the various organs of the 

 body, and has been termed by Lankester a haemocoel. The 

 theory of Phleboedesis formulated by Lankester to account 

 for the development of the haemocoel is as follows : 



