APPENDIX. ' 177 



being that the entire colony is forced along, at the same time revolving 

 upon its long axis. 



42. Page 81. Panceri says, "Each zooid has two luminous spots, 

 which are situated over the position of the ganglia of the nervous 

 system; and there are loops like cords passing over the narrow end, 

 connecting them." 



43. Page 94. Dr. Gunther expressed the view that the organs are 

 the producers, not the receivers, of light. He says, in brief, that the num- 

 ber of pairs of small globular bodies found along the abdominal profile 

 is in direct relation to that of the vertebrae, the muscular system, etc. 

 These are of two kinds. One class consists of the anterior, bi-convex, 

 lens-like body, which is transparent during life ; simple, or composed of 

 rods, and coated with a dark membrane composed of hexagonal cells or 

 rods arranged as in a retina. This structure characterizes the plates of 

 Stomias (Plate XX.), Astronechtes, Chauliodus (Plate XXI., Fig. 4). 



In the other set, as found in Gonostoma, Mycloplum mausolicus, and 

 Argyopelicus, the organs have a simple, glandular structure. Branches of 

 spinal nerves have been traced to each organ, and are distributed over 

 the retina-like membrane of the glandular follicles. 



The difference in structure of those organs naturally produces differ- 

 ence of opinion regarding their functions ; but Gunther believes that all 

 the organs iu their functions have some relations to the conditions of 

 light in which the fishes that possess them live. Three principal tl)eories 

 regarding them are given : first, they may all be accessory eyes ; second, 

 only the oi'gans with the lenticular body are eyes, and those with glands 

 are light-givers ; third, all are producers of light. Many arguments have 

 been advanced to support these different hypotheses ; but it would seem 

 that the second view is most tenable, from the fact that the organs with 

 the retina-like membrane bear a great resemblance to a true eye, and 

 finally the glandular organ in the little fish Mycloplum has been seen 

 to gleam with a phosphorescent light. Dr. Gunther thinks it not 

 improbable that the compound orgian is an accessory eye, and a light- 

 producer as well. The light, he says, may be produced at the bottom of 

 the posterior chamber, and emitted through the lenticular body in par- 

 ticular directions, with the same effect as when light is sent through the 

 convex glass of a bull's-eye. 



