\ 12 GENERAL CONCEPTS 



sequence. 1 he removal ot the eyestalk resuhs in premature moUing and 

 in more frequent successive molts. 11 sinus glands Irom other crabs are 

 transplanted to crabs without eyestalks, molting is delayed. Thus, the 

 sinus gland in the eyestalk produces a hormone which inhibits and 

 delays molting. 



There is evidence for the hormonal control of the development of 

 secondary sex characters in members of many different invertebrate 

 phyla. When the gonads are removed surgically, or destroyed by para- 

 sites, the sex characters either fail to form or regress if present initially. 

 There is some evidence that the sinus gland of crustaceans and the 

 corpora allata glands of insects secrete hormones which regulate the 

 activity of the ovaries and thus are analogous to the gonadotropic hor- 

 mones secreted by the vertebrate pituitary gland (p. 626). 



Certain aspects of tissue metabolism in some invertebrates appear 

 to be regulated by hormones, but there is no clear evidence as yet of 

 any effect of a vertebrate hormone on invertebrate tissue metabolism. 

 The sinus gland of crabs secretes a hormone which decreases basal meta- 

 bolic rate, for there is an increase in oxygen consumption following 

 removal of the sinus gland and a return to the normal rate following 

 injection of extracts of the glands. The sinus gland hormone produces 

 an increase in blood sugar concentration when injected into crabs, pro- 

 viding another interesting parallel between the sinus gland secretions 

 and those of the vertebrate pituitary. 



Hormones play a role in determining pigmentation in the octopus, 

 squid, crabs, insects, fish, amphibia and reptiles. In most animals, color 

 changes are produced by streaming movements of the pigment-laden 

 cytoplasm of the color cells (chromatophores). The chromatophore cell 

 of the cephalopod has smooth muscle fibers attached in such a way that 

 their contraction spreads out the pigment-containing cytoplasm. Crus- 

 taceans can be separated into two major groups, those that darken and 

 those that lighten when the eyestalk is removed. Injection of eyestalk 

 extracts has diametrically opposite effects in the two types, because of 

 basic differences in the responses of the chromatophore cells. More 

 recent experiments have shown that there are at least three different 

 chromatophore-regulating hormones in crustaceans. 



A number of endocrine organs are very closely associated with the 

 nervous system and undoubtedly evolved from such tissue; others evolved 

 independently of the nervous system. It would seem useless to try to 

 argue which is the more "primitive" coordinating system— nervous or 

 endocrine. Both had their earliest traces in very primitive, single-celled 

 animals and each type evolved independently of the other to their 

 present state. 



Questions 



1. Distinguish the types of animal nutrition. Give an example of each. 



2. Discuss the similarities and differences of the process of digestion in ameba, planaria, 

 earthworm and man. 



3. What is the function of: the rumen, the gizzard, the pancreas, the atrium and the 

 hemocoel? 



