96 



COMPARATIVE PHYSIOLOGY 



up during the period when the new shell is being formed and 

 the animal is temporarily deprived of the power to feed. 



Amylolytic enzymes have been found in the alimentary 

 tract of all animals investigated with this end in view. In 

 the coelenterates mentioned, Bodansky and Rose found that 

 an amylase and a maltase were present but lactase was absent. 

 On the other hand, both sucrose and lactose are digested by 

 extracts of the digestive gland of the lobster. 



A remarkable phenomenon connected with starch digestion 

 in the invertebrate phyla is presented by the structure 

 known as the crystalline style present in most lamelli- 



Digestive gland 



stomach 



style 



heart 

 Fig. 24. — The crystalline style of the bivalve mollusc. 



branchs and in a few prosobranch gasteropods. The crystal- 

 line style is an elongated hyahne rod of proteinous nature to 

 which is absorbed an amylolytic enzyme. It lies freely either in 

 a groove of the intestine or in a separate diverticulum, revolving 

 about its axis in the ciliary current produced by the epithelium 

 of its sac. As it revolves its anterior end, which in many forms 

 projects into the stomach, is worn away against a horny plate 

 (the gastric shield) in the dorsal wall of the latter, entangling 

 in its motion a mucous mass laden with diatoms and inorganic 

 debris. In some forms it is broken down and reformed 

 periodically ; in the Eastern oyster (Nelson) it disappears 

 an hour after the fall of tide, and may be reformed in fifteen 



