690 SUMMARY OF CURRENT RESEARCHES RELATING TO 



of T. raymondi and Nuttallina thomasi are kept in favourable conditions 

 as regards abundance of nourishment, they attain sexual maturity within 

 one year. 



Land and Fresh-water Shells of the Bahamas.* — W. H. Dall 

 describes a collection of these shells, amongst which are several new 

 forms. In a general way each group of islets, or each island inhabited 

 by land shells has its characteristic forms of pulmonate molluscs. Some 

 few forms are widely distributed, but others, especially Cepolis and Cerion, 

 are for the most part very local, with a few widely distributed species. 



y. Scaphopoda. 



Structure of Dentalium.f — Arcangelo Distaso communicates notes 

 on the minute structure of the foot, the respiratory organs, the osphra- 

 dium, the reno-pericardial opening, the heart, and the hypobranchial 

 gland of this interesting type. 



Anatomy and Histology of Dentalium.J — Maria Boissevain gives 

 some details on this subject, several of which are here enumerated. The 

 foot is covered with a ciliated epithelium, and upon it unicellular glands 

 are present. On the edge of the mantle are pigment-spots, and on the 

 inner side of its anterior border there is a zone of sensory epithelium. 

 The gut musculature consists of a thin layer of circular fibres. There is 

 a taste sac in the subradular organ. The communication between the 

 sex glands and the kidney must arise anew at every sexual period. In 

 the region where the communication is made, there lie peculiar groups 

 of cells, about the nature of which nothing is known. 



8. Lamellibrauchiata. 



Growth of Oysters.§ — 0. C. Glaser has made experiments to ascer- 

 tain (1) whether normal oysters can be converted into elongated ones by 

 pressure ; (2) whether elongated oysters liberated from an oppressive 

 environment will change in shape ; and (3) whether the recuperative 

 powers of elongated oysters varies with their age. 



His answers, briefly stated, are the following : — The elongated con- 

 ditions often exhibited by young oysters is due to crowding. But old 

 oysters normally become " razor-blades." The crowded young forms 

 may be said to be in a state of premature old age. When removed from 

 crowded conditions, their growth in width is rapid for a considerable 

 time. The recuperative power varies with age. Young individuals 

 recover much more rapidly than old forms, though these, too, improve to 

 a marked degree. 



Derivation of North American Unionida3.|| — C. A. White discusses 

 the origin and distribution of fresh-water mussels in North America. In 

 particular he brings forward evidence to show that the well-known types 



* Smithsonian Misc. Coll., xlvii. (1905) pp. 433-52 (2 pis.). 



t Zool. Anzeig., xxix. (1905) pp. 271-8 (6 figs.). 



X Jena Zeitschr., xxxviii. (1904) pp. 553-72 (3 pis.). 



§ Johns Hopkins Univ. Circ, No. 3 (1905) pp. 226-40 (1 pi.). 



|| Smithsonian Misc. Coll., iii. (1905) pp. 75-88 (6 pis.). 



