2o6 ARTHROPODA 



alimentary canal Is short and straight. The stomach and intestine 

 send out lateral tubular or bladder-like expansions. 



There are many species o^ parasitic Arthropoda. Fish lice (crus- 

 tacea) are external parasites and suck in nourishment. Rhizo- 

 cephala, such as Sacculina, send ramifying absorptive roots through 

 the body of the host. But in insects and arachnids we find parasi- 

 tism most highly developed. 



Respiration.^" — In water-breathing Arthropoda we find modified 

 appendages (gill-books of the king crab) or well-developed gills 

 such as in the lobster. The air breathers have a highly developed 

 tracheal system opening to the exterior by paired spiracles or 

 stig?7iata. 



Circulatory System. — The system of circulation of Arthropoda is 

 not closed but an open one with sinuses playing an important part in 

 the collection of impure blood. The heart is usually elongated and 

 dorsally situated in Arthropoda. The Crustacea (lobster) have a 

 shield-shaped heart just posterior to the stomach. The blood enters 

 t\vQ pej'icaj-dial iinus and passes into the heart by several pairs of ostia 

 which have valves. Arteries leave the heart and pass to the inter- 

 cellular spaces. 



The orange color of the blood of the prawn, and the yellow 

 color of the insects' blood are perhaps due to carotene, according 

 to A. C. Redfield. The green blue color of the blood of a lobster 

 is due to hemocyanin. 



The role of carotene, a highly unsaturated hydrocarbon (CgoHse) 

 as an important agent in holding and slowly emanating absorbed 

 radiant energy, is a subject that interests the author of this text. 

 (P. 442.) 



Excretion. — In Insects and Arachnids there are excretory tubules 

 (Malpighian tubules) which communicate with the intestine. In 

 the lobster and allied Crustacea, the paired green glands send their 

 secretion out from pores at the bases of the antennae. 



Nervous System. — In Arthropoda the cerebral and sub- 

 esophageal ganglia have developed highly. We also find that the 

 thoracic ganglia are large and show the efi'ects of a lateral fusion. 

 The nerves in the thoracic region are especially well developed. On 

 the whole the nerve cord reminds one of that of the Annelid but is 

 more highly developed. 



*° Lee, M. O. 1929. Respiration in the insects. Qu. Rev. of Biol., vol. 4, no. 2, 

 pp. 213-232. 



