THE PINEAL BOD Y 27 



4. The pineal region in teleosts 



In teleosts the parapineal organ does not appear and the 

 pineal organ itself is present only in a seemingly retrogressive 

 condition. During the early stages of development, however, 

 in a few forms there is an anlage of the parapineal organ. The 

 lamina supraneuroporica is, if anything, more broad and more 

 pronounced than in the ganoids, but it differs from this structure 

 in the latter forms in the fact that it is not vascular nor does it 

 come into relation with any vascular network. A paraphysis 

 does not develop, as a rule, or if it does occur, it only appears 

 as a small evagination from the roof-plate, as in Belone acus. 

 Not infrequently in the earlier stages of development in Lophius, 

 the paraphysis appears as a small bud in the roof region. In 

 the larval forms of some species, as, for example, Anguilla and 

 Cepola, the paraphysis has the form of a very small evagination 

 from the roof consisting of a thin wall, but is not vascular and 

 in no way connected with a vascular net. The velum trans- 

 versum is a simple, flat, transverse fold which is not in connec- 

 tion with the chorioid plexus in any portion. In certain in- 

 stances this element is very little developed and may, in a few 

 cases, be entirely absent. The dorsal sac is, as a rule, very large 

 and presents itself in several different forms. Frequently it is 

 thrown into many folds, particularly the portion representing 

 the superior wall and in these folds are found numerous blood- 

 vessels in a plexiform arrangement. Sometimes the sac along 

 its caudal wall is grooved in the midsagittal plane and in this 

 groove rests the stalk of the pineal organ. An anterior inter- 

 calated portion is absent, but a well-marked habenular com- 

 missure is always observed. Following this commissure is the 

 pineal organ and caudal to it a short pars intercalaris posterior 

 followed by the posterior commissure (fig. 3). 



Among the early workers in this region in teleosts are listed 

 some of the great pioneer names in morphology. Albrecht 

 Haller in 1768 165 described the epiphysis in the carp, but did 

 not find it in the trout. Cuvier in 1845 77 also observed it in 

 teleosts, and Carus in 1814 59 found it to be a saccular formation 

 extending from the dorsal .region of the brain. Tiedemann 39 ^ 



