670 SUMMAltY OF CUKRENT llESEAliCHES KELATING TO 



Comparative Anatomy of Mammalian Ear-cartilage.* — J. E. V. 

 Boas describes the cartilage of the external ear in a number of mammalia. 

 In the placental mammals there is a common type with a definite number 

 of indentations and lobes. Though variously modifiable, and with the 

 parts very unequally developed in different forms, yet even to details 

 they are found to agree in types so far apart as pig and dog. This 

 agreement as to type holds good for degenerate ears also. 



Tunicata. 



Embryology of Oikopleura.t — K. Kellner describes certain embryos 

 of an Oikopleura which occur " rooted " in the tail of adults. They 

 form little pear-shaped bodies and were previously, but erroneously, 

 regarded as gland-cells. The eggs are smaller than those of any other 

 known Tunicate, and the embryos evidently are parasitic upon the 

 adults, drawing nourishment through a root-like process. They occur 

 in large numbers on the south coast of Florida. 



INVERTEBBATA. 



Mollusca. 



Mollusca of the Ozarkian Fauna.| — H. A. Pilsbry and James H. 

 Ferriss give an annotated list of the species of Mollusca of the Ozark 

 Mountains, Arkansas, and discuss the faunal relations of this region. 

 Its topography affords conditions favouring the evolution of special 

 forms, and many have probably been evolved where they now occur. 

 About ;-)6 p.c. of the total number of land snails listed are peculiar to 

 the region. Some aquatic forms, Unionidte and Pleuroceratidfe, are 

 also characteristic, although in the main Mississippian species rule. 



7- Gastropoda. 



Molluscan Radula.§ — Igerna B. J. Sollas has investigated the 

 chemical composition of the radula in a number of Molluscs. In all, 

 the radula has an organic basis of chitin ; the Docoglossa are unique 

 among Mollusca in the composition of their teeth, of which the most 

 important constituent is silica hydrate or opal. All the other groups, 

 including the Rhipidoglossa, form a second type in which the radular 

 chitin is hardened superficially by deposits containing calcium, iron, and 

 phos'phoric acid, which, together, perhaps with an additional organic 

 substance, form that outer covering so long known as the enamel layer, 

 but hitherto unexplained. In the Chitonid^e ferric oxide is the most 

 important mineral constituent, and is the cause of the dark colour of the 

 teeth. Some facts are given regarding the development of the radula, 

 e.g. as to the microscopic changes in the teeth subsequent to their 

 formation. These changes point to the secretory nature of the roofing 

 epithelium of the radula sac. 



* Anat. Anzeig., xxx. (1907) pp. 434-42 (6 figs.). 



+ Zool. Anzeig., xxxi. (1907) pp. 653-4 (2 figs.). 



I Proc. Acad. Nat. Sci. Philadelphia, Iviii. (1906) pp. 529-67 (3 pis.). 



§ Quart. Journ. Micr. Sci., li. (1907) pp. 115-36 (1 pi.). 



+ 



