636 REGENERATION AND GROWTH 7 



In effect the delay in moulting in the cockroach results in some retardation of 

 normal growth, and in Crustacea the sinus gland (Hanstrom, 1938; Scharrer, 

 1955) similarly has been found to mediate a retardation of normal growth vmder 

 the stimulus of regeneration-activity (Kamps, 1937; Hanstrom, 1938). 



The sinus gland also controls regeneration itself. Light stimulates the release 

 of honnone from this eye-stalk organ and the hormone retards both normal growth 

 and regeneration (Bliss, 1954a); both are accelerated in darkness, — until the 

 hormone begins to overflow from the gland spontaneously (Bliss, 1954b). The 

 gland depresses N-flow (Needham, 1955) and so presumably retards the early 

 R-phase of the regeneration- and growth-cycles. It does not delay but, as might 

 be expected, accelerates, the final P-phase of the moult-cycle (Carlisle and 

 Dohrn, 1953). 



Certain large cells, probably incretory, in the brain of earthworms, multiply 

 and grow after wounding of the body (Hubl, 1953). An endocrine function during 

 regeneration has been suspected also for the cerebral organ of some annelids 

 (Harms, 1947-9)- 



Claims that vertebrate hormones significantly affect regeneration in inver- 

 tebrates, e.g. pituitary (Hanko, 1912; Blumberg 1940) and thyroid (Weimer et 

 al., 1938; Hanstrom, 1938) have been denied by others (Paulain, 1938). It seems 

 doubtful if the protein-hormones can survive, active, in taxonomically remote 

 species, but recent careful work of Srinivasan et al., (1955) indicates that thyroxin, 

 and therefore probably other simple active principles, may retain some relevant 

 activity in invertebrates. 



(c) Chemical factors produced by regenerating tissues 



There is now much evidence that regenerating tissues themselves produce pro- 

 motor and inhibitor substances, the former in early stages and the inhibitor in 

 the later ones, so that they are probably components of an autoregulatory system. 

 As in plants (Haberlandt, 1922; English et al., 1938), a promotor substance may 

 be liberated by the damage of wounding (Needham, 1941; Thornton, 1949), 

 immediately and briefly, but indispensably for the whole subsequent train of 

 events. Extracts of damaged cells induce supernumerary growths, in planarians 

 (Loofbourow et al., 1939). Probably all damaging agents, including colchicine 

 and short-wave radiation, accelerate regeneration in low dosage. Mechanical 

 trauma stimulates growth even when inflicted on cells isolated in vitro (Fischer, 

 1930; Suntzowa, 1944). The limbs of adult Anura have been induced to regener- 

 ate by excessive mechanical or chemical trauma (Rose, 1942, 1944, 1949; Pole- 

 zhayev, 1946, 1949). The effective stimulus for the release of this factor is damage, 

 not the removal of tissue, since various types of trauma, without amputation, 

 induce supernumerary "regenerates" (Goldsmith, 1940; Fedotov, 1946; Ruben, 

 1955; Butler and Blum, 1955). Such abnormal "growths" may be induced even 

 in the unicellular Protozoa (Tartar, 1954) so that the factor is not necessarily 

 "spilled" from damaged cells and is probably bound to the proteins, locally. 

 Although Arthropods appear not to produce a wound-factor (Needham, 1947a, 

 1950a; Bodenstein, 1955) quite frequently they develop supernumerary limb- 

 regenerates (Bateson, 1894; Needham, 1950a; Wigglesworth, 1954). 



