300 PHYSIOLOGICAL CONTROL IN ANIMALS 



eggs and pupae of lampyrids. Apart from these instances, in which 

 control appears to be lacking, some form of regulation of light emis- 

 sion is the rule (Buck, 1948; Harvey, 1952; Davenport et al., 1952). 

 In the evolution of animals, effectors have preceded neural regu- 

 lation, as emphasized by Parker ( 1919 ) . This condition is still existent 

 in two phyla, the Protozoa and Porifera. 



Regulation of Luminescence in Absence of Differentiated 



Nervous System 



The Protozoa are sensitive to a multiplicity of environmental 

 agents, to which they respond mechanically, by changes in body 

 shape, movement of organelles, and chemically, by secretion and by 

 light production. In Noctihica, which has been most studied, lumi- 

 nescence is evoked normally by mechanical stimulation, resulting in 

 a brief flash; and with interrupted induced current the animals flash 

 on the first shock and remain glowing thereafter. 



These observations pose several problems, which are not neces- 

 sarily peculiar to Noctihica, nor to the luminescent reaction. Local 

 and gentle tactile stimulation results in luminescence only in the 

 region of the cell affected. A generalized luminous response, there- 

 fore, depends upon agitation of the whole cell, or transmission of 

 excitation. Photogenic granules are believed to lie superficially in the 

 cell. However, propagation of an excitatory wave may well be other 

 than a surface phenomenon; and an analogy is at hand in transmission 

 of excitation across a muscle fiber, the contractile proteins of which 

 lie within. It is, perhaps, relevant that punctured and collapsed Noc- 

 tihica, with injured membranes, give normal luminescent responses 

 to mechanical and electrical stimuli (Robin and Legros, 1866; Allman, 

 1872; Massart, 1893; E. B. Harvey, 1917). 



Another approach to this problem, full of interest, may be indicated 

 here. There are several metazoan groups in which eggs and larvae 

 are luminescent, preceding or following establishment of innervation. 

 In ctenophores, eggs and early segmenting stages light up when 

 stimulated, either by a mechanical disturbance or an electrical shock. 

 Larvae of the polychaete Cliaetopteriis also luminesce when agitated, 

 but these are metamorphosing trochospheres in which a larval nerv- 



