116 KINETIC HORMONES — II 



gastropods, such as the whelk, Buccinum, or in intermittent 

 browsers hke the snail. Helix, which do not have food continually 

 in the digestive tract. In the latter, it has long been known (Krijgs- 

 man, 1928) that the rhythm of secretion of both the buccal glands 

 and of the digestive diverticula can be accelerated by the presence 

 of food in the mouth and crop; but the mechanism by which 

 secretion is stimulated seems never to have been investigated. It 

 may be nervous ; but if not, it may be a direct chemical effect from 

 the food, or it may possibly be due to a hormone, as in vertebrates. 

 Other molluscs in which hormones might be expected are the free 

 swimming cephalopods, such as the squid, Loligo. Unlike Octopus, 

 which can retire into a crevice and digest its meals at leisure, 

 Loligo must complete its digestion rapidly. The successive phases of 

 digestion (Bidder, 1950) and the secretion of a number of enzymes 

 (Romijn, 1935) must be co-ordinated with considerable accuracy. 

 The control may well be nervous in animals with such a well- 

 developed nervous system; but other kinetic hormones exist in 

 Eledone (§ 3.12), and might well be sought in the gut of Loligo 

 and of the cuttlefish. Sepia. 



The case of the posterior salivary glands of Octopus vulgaris is 

 anomalous, and so far unexplained (Bacq, Fisher and Ghiretti, 

 1952). The natural saliva yields 5-hydroxytryptamine, which 

 appears to stimulate secretion of these salivary glands; but the 

 secretion produced is abnormal, in being clear instead of viscous, 

 containing no poison, and causing inhibition of the heart instead of 

 stimulation. It seems possible that the salivary extract acts upon 

 the gland by causing constriction of its blood vessels, rather than 

 by stimulating its natural secretion. 



Arthropoda. The crayfish, Astacus, is another invertebrate 

 which secretes digestive enzymes periodically in relation to times 

 of feeding ; but the secretion follows a burst of mitotic activity in 

 the gland and is produced by the breakdown of the new cells that 

 result (holocrine secretion; Hirsch and Jacobs, 1930). According 

 to the classification of hormones used in this book, such a process 

 is one of growth that might be controlled by a morphogenetic 

 hormone, but not by a kinetic hormone (cf. submaxillary gland of 

 rat. Part II, § 3). In the beetle Tenebrio, it has also been found that 

 a "factor" in the blood is associated with increased mitosis in the 



