cxliv GENERAL SUMMARY OF SCIENTIFIC AND 



The Ophiurans have been further discussed by Mr. Lyman in 

 the Bulletin of the Museum of Comparative Zoology. 



In the department of Mollusca, we have several papers on 

 their embryology by German observers. In the Nieder- 

 Icmdlsches Archiv fiir Zoologie, Vol. L, Part L, is a paper by 

 Dr. Emil Selenka, the editor, on the " First Formation of the 

 Embryo in Tergipes claviger" illustrated by a plate. In Part 

 II., the same author has a paper on " The Primitive Layers of 

 the Embryo in Purpura lapillus" also well illustrated. Both 

 these papers belong to the newer embryology; that is to say, 

 the author occupies himself with the exact following out of 

 the origin and disposition of the cellular elements of the em- 

 bryo. In his paper on Purpura, Dr. Selenka proposes to dis- 

 tinguish two modes of formation of the blastoderm "epi- 

 boly" and "emboly." The former is accompanied by the 

 presence of a large food-yelk, and the egg is consequently 

 meroblastic, or partially so. The first formative cells grow 

 over the partially segmented or wholly nnsegmented colored 

 yelk. In emboly, the egg is holoblastic, and a pushing in of 

 the cells of the primitive blastosphere takes place. 



Dr. Salensky, of Kasan, has a paper, with several plates, on 

 "The Development of the Prosobranchiata," in Siebold & 

 Kolliker's ZeitscJirift, Part IV., for 1872, which has much in- 

 teresting matter on the " Veliger" larval form of various 

 genera, but does not deal with the histogenesis. 



"The Development of Gastropoda qpisthobranchiata" is 

 the title of a paper by Dr. PaulLangerhaus in the same jour- 

 nal, Part II., for 1873, in which some points in the early devel- 

 opment of Acer a bullata, Doris, and JEolis peregrina, are short- 

 ly treated from the point of view of the germ-layer theory. 



Mr. Lankester read a paper before the British Association 

 " On the Genealogical Importance of the External Shell of 

 Mollusca," in which he attempts to show the typical form of 

 the immense variety of shells, and especially to homologize 

 the pen of the cuttle-fishes with the shells of the lower Mol- 

 lusca. 



In descriptive malacology, Mr. Dall presents a paper on 

 the shells of Beh ring's Strait, and numerous exotic species 

 are described in foreign journals. Mr. Conrad describes two 

 new fossil shells from the Upper Amazon, at Iquitos, one 

 hundred miles west of Pebas. They were collected by Pro- 



