80 KINETIC HORMONES — I 



evidence of the action of a concentrating hormone has been 

 reported (Welsh, 1939). 



Movement of pigment due to change in shape of distal retinal cells 



Change in cell shape in the prawns Palaemonetes and Leander 

 and in a Bermudan shrimp Anchistioides is brought about by con- 

 tractile fibres (Welsh, 1936). The distal retinal cells here lie in 

 the same position round the cones of the ommatidia, as in Cam- 

 barus; but if the usual pigment migration occurs, it is obscured 

 by such a surging inwards or outwards of the protoplasm that, even 

 the nucleus is moved as well as the pigment granules, and the whole 

 cell appears to change shape (Fig. 3-13fl). If the pigment is 

 dissolved away, fibres in these cells can be seen to cause the 

 inward pigment movement by their contraction (Welsh, 1930; Fig. 

 3-13^). It may be noted that physiologically the same effect is 

 produced by this fibre contraction as by pigment dispersal in 

 Cambarus (Fig. 3- 12c), yet these would appear to be opposite 

 reactions in terms of contraction of protein molecules. 



Much work on Palaemonetes and Leander has confirmed the 

 action of a retinal-light-adapting hormone, from the sinus 

 GLAND. This has been found to be similar to that in such Brachyura 

 as Cancer and Uca (Kleinholz, 1936); but it is not clear if it is the 

 same as RPDH of Cambarus. Evidence for an antagonistic, 

 RETINAL-DARK-ADAPTING HORMONE has been found in Palae- 

 monetes, and the richest extracts have been obtained from the 

 TRiTOCEREBRAL COMMISSURES (§ 2.112; Brown, Hiucs and Finger- 

 man, 1952). 



A persistent diurnal rhythm of movement of distal retinal cells 

 has been shown, at least in continuous darkness, for Anchistioides 

 (Welsh, 1936), Palaemonetes (Webb and Brown, 1953), and 

 Leander, Praunus and Pandalus (Bruin and Crisp, 1957); for this 

 a hormonal control has been postulated. It is not inhibited by 

 sinus gland removal ; but it is probable that the sinus gland is, as in 

 other cases, only the storage organ for the hormone, of which 

 sufficient is still secreted from the source in the ganglionic-X- 

 organ (§ 2.112) to maintain the rhythm. 



Changes in distal retinal pigment of grapsoid crabs (R. I. 

 Smith, 1948) are very similar to those in prawns, with a marked 



