The brain of Acipenser. 223 
of EDINGERS Vorlesungen (5th ed., fig. 77) suggests that a condition 
similar to that in Acipenser obtains in Scyllium. It would be inter- 
esting to know whether the entodermal portion of the hypophysis 
comes into closer relations with the saccus than does the ectodermal 
portion, and whether the saccus tubes penetrate only into the ento- 
dermal portion. 
Nerve elements have been described in the saccus by several 
authors. Krause (Mikr. Anatomie, p. 437, cited by KÖLLIKER, 96, 
p. 603) describes fine varicose fibres descending into it from the 
walls of the infundibulum. Ramon (94, cited by KÖLLIKER, ‘96, 
p. 604) describes in the mouse fibres coming from a nucleus situated 
behind the chiasma and forming a close plexus throughout the whole 
saccus. BERKELEY (95) describes several forms of cells in Mammals, 
including cells of the II type and cells with several neurites. The 
neurites were traced toward the infundibulum but were not traced 
into it. BiCKFORD (95) in a paper on the hypophysis of Calamo- 
ichthys, in which she seems to have wrongly identified the various 
structures concerned, mentions processes presumably from nerve 
cells, running from the corpus mammillare down among the tubes 
of the saccus. EDINGER (92) found in Selachians a bundle of coarse 
(medullated ?) fibres coming from the dorsal part of the ‘tween brain 
(or mid brain?), crossing at the point of separation of the lateral 
lobes and infundibulum, running backward into the saccus and 
breaking up there. He thinks that these fibres are very probably 
connected with those in the hypophysis. 
The fibres described by KRAUSE and Ramon probably cor- 
respond to those which enter the saccus in Acipenser from the 
cephalic wall of the inferior lobes and form a plexus beneath the 
epithelium of the saccus (page 125). There is nothing in Acipenser 
that could correspond to the fibres described by EDINGER. He has 
apparently not found these in other Vertebrates than the Selachians. 
It is impossible to compare the structure described by BERKELEY 
or any part of it with the apparatus in Acipenser. What is prob- 
ably the most important part of the nervous apparatus in the saccus 
of Acipenser which has not been described before. I refer to the ciliated 
cells and their fibres which end in what I have called the nucleus 
of the saccus bundle in the ‘tween brain (page 114). 
RABL-RÜCKHARD (83) describes the saccus and hypophysis in 
the trout. He considers the saccus a tubular gland which is prob- 
ably engaged in the production of cerebro-spinal fluid, or at least 
