THE PINEAL BODY 103 



The walls of the organ have, in addition to the usual ependymal 

 cells, some special sensory cells. In the lumen are free cells with 

 no particular syncytial formation. 



In the ganoids no mention is made of any evidence indicative 

 of glandular activity. Six ganoids in all have been carefully 

 studied and in only one, as already stated, are there signs of the 

 parapineal organ, namely, in Amia, otherwise all species present 

 a pineal organ which is not as well developed as in the selachians. 



4. Comparative anatomy and histology of the epiphyseal complex 



in teleosts 



The epiphyseal complex in teleosts differs from that in selach- 

 ians and ganoids in its greater size. In some forms, however, 

 it is only rudimentary, being but a solid bud, while in others, 

 it is a complicated end-sac. It is never in any case like an eye 

 and seldom does it come into relation with the surface of the 

 head as in the cyclostomes. The number of species already 

 examined is perhaps too limited to make certain of all of these 

 observations. The only part of the epiphyseal complex which 

 develops and appears in the adult is the pineal organ. In a few 

 instances, during the very early stages of development, there 

 is present what may be considered the anlage of the parapineal 

 organ. The parts which the pineal organ presents in teleosts 

 are an end-vesicle, a stalk, and an ill-defined proximal portion. 

 In many instances the stalk is short and the end-sac large. In 

 most species the end- vesicle is pear-shaped and connected with 

 the roof by a hollow stalk. The walls of the end- vesicle are 

 either flat or formed into many folds, thus producing lateral 

 diverticula and giving the sac the appearance of a tubular gland. 

 In some cases the end-vesicle does not develop as such, the pineal 

 organ being a broad sac connected with the brain by a slightly 

 constricted area. The entire pineal organ may be a rudiment 

 as in Syngnathus, where it is almost solid throughout its entire 

 extent. The vast majority of the cells in the end- vesicle are 

 small and set closely together. Some cells have an epithelial 

 arrangement: these are doubtless neui;oglia. The presence cf 



