June 12, 1908] 



SCIENCE 



913 



clearly separated from the motor root by 

 the intervening lateral groove of the brain. 

 This groove separates the dorsal and ven- 

 tral halves of the brain wall (Fliigelplatte 

 and Grundplatte, His) ; the sensory root and 

 the mesencephalic bundle are dorsal to this 

 groove, the motor root ventral to it. The 

 sensory and motor portions of the trigem- 

 inus are at this time widely separated. At 

 the level of the exit of the fourth nerve the 

 mesencephalic bundle holds a position be- 

 tween the central and peripheral limbs of 

 the trochlearis which is characteristic for 

 all vertebrates. Dorsal to the peripheral 

 limb of the trochlearis, however, is to be 

 seen in the human embryo a large bundle 

 which runs from the tectum mesencephali 

 into the cerebellum, the tr. tectocerebel- 

 laris which occupies this same position in 

 lower vertebrates. Hence, the cutaneous 

 sensory fibers are distributed through the 

 whole length of the dorsal half of the brain 

 wall as far forward as the superior col- 

 liculus. The roof of the midbrain is still 

 in part a primary cutaneous sensory center, 

 even in man. This gives the strongest 

 morphological support to the account of 

 the evolution of the cutaneous, auditory 

 and visual primary and secondary reflex 

 centers and the cerebellum out of a primi- 

 tive longitudinal column or zone whose 

 functions were at first simple cutaneous 

 sensory. 



The Epibranchial Placodes of Ameiurus 



melas and nebulosus: F. L. Landacee, 



Ohio State University. 



The epibranchial placodes in Ameiurus 

 arise just posterior to the dorsal portion 

 of each gill slit and give rise to elements 

 in the cranial ganglia quite distinct from 

 those of the dorso-lateral placodes and of 

 the neural crest. 



The ectodermal area in which the pla- 

 codes occur is indicated first by active 

 mitosis and later by a process of prolifera- 



tion which is almost complete; and the 

 ganglion is almost detached from the ecto- 

 derm before it comes into contact with cells 

 from the dorso-lateral placode and neural 

 crest except in the case of the third divi- 

 sion of the tenth nerve. 



The placodal portions of the seventh, 

 ninth and first two divisions of the tenth 

 nerves have been followed to a late stage 

 and give rise to the portions of these gan- 

 glia which furnish communis fibers to these 

 nerves. 



Whether the epibranchial ganglia fur- 

 nish gustatory fibers only or general vis- 

 ceral fibers also has not yet been certainly 

 determined, but the evidence is very strong 

 that they give rise to special visceral or 

 gustatory fibers only. 



The direction of proliferation of the pla- 

 codal cells is backward, and their first con- 

 nection with the remaining portions of the 

 cranial ganglia is by means of a delicate 

 intermediate cell mass. 



Pinkus's Nerve in Amia and Lepidosteus: 



Chas. Brookovee, The University of 



Chicago. 



Search for Pinkus's nerve in adult Amia 

 by macroscopic and microscopic methods 

 failed to show the root which Allis de- 

 scribed running back to the f orebrain. The 

 ganglion was found as Allis described it in 

 larval Amia. A similar ganglion was found 

 in larval stages of Lepidosteus osseus. The 

 cells of the ganglion become scattered in 

 Amia after the 50 mm. stage, when there 

 are two hundred and fifty cells. In adult 

 Amia the large cells from the larval gan- 

 glion were recognized to the number of one 

 thousand on each olfactorius. They have 

 the appearance of functional nerve-cells 

 among the olfactory fibers as the latter 

 break up into small bundles to enter the 

 Schneiderian membrane. 



There is some evidence that the cells are 

 those of a sympathetic ganglion in Amia. 



