432 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Accessory Fins in Raia batis.* — J. Rennie records two cases of 

 Raia batis in which in the mid-dorsal line there occurred accessory fins 

 of somewhat complex structure. Although median in position, they 

 appear to be of the nature of paired fins. In one a combination of fin 

 structures occurred which is representative of different phylogenetic 

 stages in the evolution of the Elasmobranch fin. 



Chorda Tympani in Microtus.j — V. E. Emmel has made out the 

 following in the development of the chorda tympani in Microtus. In 

 the earlier stages it passes behind and underneath the spiracular cleft. 

 In later stages it occupies a position over and in front of the closed end 

 of the spiracular cleft. It is, therefore, a post-spiracular nerve, and is 

 to be considered as the homologue of a post-trematic nerve of fishes and 

 amphibians. 



Jaw and Branchial Muscles in Elasmobranchs4 — G. E. Marion 

 describes the mandibular and pharyngeal muscles of Acanthias and Raia. 

 In the latter, as might be expected from its shape, a few muscles are 

 developed which are not found in the dogfish. These are the levator 

 and depressor of the rostrum, and the cerato-hyomandibularis, which 

 from its position seems adapted to the protrusion of the jaws. Apart 

 from these the two forms studied agree very closely. The deeper ventral 

 longitudinal muscles of Raia are described for the first time. 



Membranous Labyrinth in Sharks.§ — Charles Stewart describes 

 this organ in five genera not dealt with by Retzius in his monograph. 

 There is a considerable resemblance in the labyrinths of Notidanus and 

 Lcemargus. In Lamna cornubica there is fusion of portions of the two 

 divisions of the utricle, forming a structure which has a ck>se superficial 

 resemblance to the sinus superioris utriculi of Teleosts ; the cavities, 

 however, remain distinct. Alopecias wipes shows a similar characteristic ; 

 here the resemblance to the Teleostean sinus is even more marked. 



Structure and Relations of Mylostoma.|| — C. R. Eastman points 

 out the intimate structural resemblance between Mylostoma and Dini- 

 c/itht/s, and, taking these forms as typical examples of Arthrodires, com- 

 pares their general organisation with that of Neoceratodus and other 

 Dipnoan fishes. Evidence is given for associating Arthrodires with 

 Dipneusti, and their relations to fossil and recent members of the sub- 

 class are considered. A summary is also given of the leading facts in 

 the evolutionary history of Dipnoans since their first appearance in the 

 Lower Devonian until their decadence, bordering upon extinction, in 

 the modern fauna. 



Acromerite of Amphioxus.1T — B. Hatschek finds that the "rostral 

 •episomite process " in Amphioxus contains an elongated cavity, extending 

 laterally to the notochord, and representing a direct continuation of the 



* Anat. Anzeig., xxviii. (1906) pp. 428-31 (2 figs.). 



t Journ. Comp. Neurol, u. Psychol., xiv. (1904) pp. 411-17. 



\ Tufts College Studies, ii. (1905) No. 1 (Scientific series) pp. 1-34. 



§ Journ. Linn. Soc. (Zool.) xxix. (1906) pp. 407-9 (1 pi.). 



|| Bull. Mus. Comp. Zool., 1. (1906) pp. 1-29 (5 pis.). 



t Morphol. Jahrb., xxxv. (1906) pp. 1-14 (1 pi.). 



