314 DISCOVERY REPORTS 



As far as I am aware none of the photophores of this type have ever been observed 

 in a state of active luminescence. 



2. THE ORGANS OF PESTA (LUMINOUS LIVER TUBULES) IN SERGESTES 



CORNICULUM KROYER.i S. SARGASSI ORTMANN, S. DIAPONTIUS 



BATE, AND S. EDWARDSI KROYER 



The organs of Pesta, or presumed internal cephalothoracic organs which occur in 

 various members of the genus Sergestes, are groups of modified liver tubules. They are 

 ventrally directed, and are closely compacted and denser than the normal liver. They 

 are first mentioned by Pesta (1918, p. 10), and an account of their appearance derived 

 from a study of dissections of freshly caught material is given by Burkenroad (1937). 

 The latter author describes the distal (ventral) parts of the tubules as being Antwerp 

 blue in colour in the living animal, the upper parts white, while the normal liver itself 

 is translucent. "That part of the tunic of the gastric gland which covers the dorsal 

 parts of the areas of modified tubules bears a dense layer of carmine chromatophores", 

 so that each photophore is "covered dorsally with a carmine cap". He also describes 

 the variation in number and arrangement of these groups of modified tubules that occur 

 in the genus, and points out that whatever their arrangement an antero-lateral pair 

 situated just above the branchial chamber and immediately behind the base of the 

 mandible is always visible externally through the transparent branchiostegite, while a 

 posterior pair of organs often show "through the gap in the lateral musculature just 

 above the branchial area of the thirteenth somite". 



According to Burkenroad, organs of Pesta "appear to be present in all members of 

 the genus other than the S. mollis, S. tenuiremus, S. robiisttis, and S. challengeri super- 

 species of Hansen's ' Group I ' ". But Welsh and Chace (1938) describe the occurrence in 

 S. tenuiremus of organs which closely parallel the structures described by Kemp (1925) 

 in three species of Pandalids from the Indian Ocean. The organs of these Pandalids are 

 almost certainly, from the description given, composed of groups of modified liver 

 tubules, closely similar to those oi Paropaudahis richardi{p. 323), and it would therefore 

 appear that the structures in Sergestes tenuiremus are organs of Pesta, in direct opposition 

 to the above-quoted statement by Burkenroad. 



Critical examination, however, of Welsh and Chace's account of these structures 

 makes it unlikely that they are truly organs of Pesta. They are described as "large, 

 whitish organs found in the coxae of the last pair of thoracic legs near the opening of 

 the vasa deferentia": each organ is composed of "a cluster of three large photophores 

 with well-developed lenses entirely enveloped by the surrounding tissues ". It is perhaps 

 possible that these organs are in reality spermatophores, since they were discovered in 

 a large male specimen : I have seen sections of Meganyctiphanes norvegica in which the 

 spermatophores had a very similar staining reaction and superficial appearance to 



1 While this work was in the press specimens identified as Sergestes corniculuni by Dr Kemp were sent 

 at his suggestion to Dr M. D. Burkenroad for his opinion. Although belonging to the " corniculum " group 

 of the subgenus Sergestes they are actually specimens of Sergestes seminudus Hansen. 



