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ANNUAL REPORT SMITHSONIAN INSTITUTION, 1963 



Neurohaemal 

 organ behina 

 the brain 



Figure 4 — The head of a prawn and, alongside it on the left, an enlargement of the 

 left eycstalk dissected to show the optic medullae of the brain (stippled), which are 

 largely concerned with visual integration. The unstippled parts of the medullae are 

 the sinus gland (above), supplied from below by three groups of neurosecretory cells. 



in other parts of the brain. The second neurohaemal organ lies behind 

 the brain and is supplied by neurosecretory fibers from cells in the liind 

 part of the brain. 



It lias long been a puzzle why there should be so many centers of 

 production of color change hormones within the brain — there are at 

 least five such centers in prawns. A possible explanation may emerge 

 if we consider the detailed distribution of these centers within the 

 brain and the functions of the various parts within which they are 

 found. Three of the main centers lie within that part of the brain 

 which is concerned with the integration of visual input. At the most 

 peripheral level we find a neurosecretory center (sending its hormones 

 to the sinus gland) which appears to receive information on the num- 

 ber and frequency of visual cells receiving the stimulus of light; per- 

 haps this center regulates the degree of darkness of the body. At a 

 second level we find a neurosecretory center in that part of the brain 

 which is largely concerned with a comparison of direct illumination 

 with light reflected from the background. This center seems to be 

 concerned with the so-called albedo or background response. At a 

 third level the pattern of things seen may result in the activation of 

 a neurosecretory center which controls pattern — a uniform pattern 

 when on a background of sand or a stripy pattern amongst seaweed, 

 for example. And the center at the back of the brain may be con- 

 cerned with a total integration of all stimuli and central effects, visual 

 or otherwise, which may lead to a color change. Thus, prawns always 



