l8o S. STILLMAN BERRY. 



Until very recently photophores on the tentacles have been 

 supposed to be of rare occurrence, but it has lately been shown 

 that they do actually so exist in quite a number of diverse forms, 

 having tended to escape observation by reason of being embedded 

 so deeply in the fundamental substances of the tentacle stalk as 

 to be quite invisible in preserved material unless thoroughly 

 cleared or otherwise specially treated. In Pyroteuihis Vivanti 

 and Mortara have recently established the presence of a series of 

 four such organs in the stalk of each tentacle. I had not only 

 independently made the same discovery in material from both 

 the Atlantic and Pacific, but had likewise found that there is 

 yet a fifth tentacular organ present, and that the same condition 

 obtains as well in the nearly related genus Pterygioteuthis. 

 Lycoteuthis and Nematolampas have two such organs in each 

 tentacle stalk. Lampadioteuthis is unique in possessing not only 

 a series of four photophores embedded in the stalk proper, but 

 in addition tucked away at its very base, a single large spherical 

 organ of peculiar structure which is quite invisible without 

 extraction of the entire tentacle from its socket. Conspicuous 

 tentacular photophores are also shown in Verrill's figures of his 

 Mastigoteuthis agassizii, 16 but the inference seems to be, as has 

 been indicated above, that these are simply of the ordinary 

 integumentary type, as seems to be true also of the tentacular 

 photophores in the genus Thelidioteuthis. 



We now come to the class of photogenic organs which is per- 

 haps the most distinctive of the Cephalopoda as compared with 

 other luminous animals, and which, next to the subocular photo- 

 phores, exhibits the most general distribution within the group. 

 Included here are a large array of very diversely constructed 

 photophores found in quite various situations upon the visceral 

 mass within the pallial chamber. These one and all, however, 

 except in the case of those myopsids which eject their luminous 

 secretion through the funnel, must naturally depend in life upon 

 the more or less complete transparency of the mantle tissues to 

 permit the unobstructed emanation of their beams. In pre- 

 served specimens, as would be expected, they can rarely be seen 

 without laying open the pallial chamber, whereupon they are 



16 Bull. Mus. Comp. Zoo/., V. 8, 1881, pl.i. 



