Literary Notices. xci 



two thirds of the thickness of the hemisphere, then to the regio-sub- 

 thalmica in the peduncular region. Irritation anywhere along this 

 tract produces the entire sequence of motions shown in the curves. 

 From this point caudad, however, coordination ceases and contrac- 

 tion of the masseter only follows stimulation. This, then, is looked 

 upon as the coordination-centre for these muscles. 



Tentacles and the Morphogenesis of the Head. 1 



An exhaustive study of the tentacles and their nerves convinces 

 the author that the tentacles of Myxine are the homologues of the 

 oral cirri of Amphioxus and the comparison further shows that the 

 ancestors of Myxine must have possessed at least eight pairs of oral 

 cirri. The branches of the ophthalmicus, the maxillaris, coronoid- 

 eus, mentalis and sub-mandibularis are nerves corresponding to several 

 segmentally arranged nerves of Amphioxus. Greater difficulties are 

 encountered in ascertaining the homologies of tentacles which occa- 

 sionally appear in Gnathostomata but it is thought that the siluroid 

 fishes present hitherto unrecognized homologies with Myxine in the 

 nervous and skeletal elements. They are of the same type and can 

 be traced back to an Amphioxus-like ancestor. 



Gegenbaur homologized the labial structures with gill bars but 

 the author regards them as the remnants of a set of organs — the oral 

 cirri. The suggestions are reenforced by hints from Paleozoic fishes. 

 Evidently comparisons with amphibia are here in order. 



Functions and Functional Development of the Semicircular Canals. 2 



The author has experimented quite extensively upon inverte- 

 brates, subjecting them to rotation in various ways, and concluded that 

 invertebrates do not exhibit those forced motions which are so charac- 

 teristic of vertebrates after rotation. There is, in fact, a sharp con- 

 trast in this respect between vertebrates and invertebrates and this is 

 attributed to the absence of the labyrinth in invertebrates. It oc- 

 curred to the author that young vertebrates, in which the labyrinth is 

 as yet undeveloped, might afford additional evidence. The tadpole 

 is a suitable subject for such experiments as the first evidence of a 

 semicircular canal appears on the io-nth day and it is not until the 



Bollard, H. B. The " Cirrhostomial " Origin of the Head in Verte- 

 brates. Anat. Anzeiger. IX, II. 



2 Schaefer, Karl L. Zeitschr. f, Psychologielu. Phys. d. Sinnesorgane . 

 VII, I. 



