clxxxii GENERAL SUMMARY OF SCIENTIFIC AND 



shell lias grown enough to cover half the embryo, which is 

 now in the so-called veliger state, the velum being com- 

 posed of two ciliated lobes in front of the mouth-opening. 

 The young oyster, as figured by Salensky, is directly com- 

 parable with the " veliger " or larva of the Cardium or 

 cockle-shell. Soon the shell covers the entire larva, only the 

 ciliated velum projecting out of an anterior end from be- 

 tween the shells. In this stage the larval oyster leaves the 

 mother, and swims around in the water, the cilia of tho 

 velum keeping up a lively rotary motion. In this stato 

 Lacaze-Duthiers observed it for forty-three days without 

 any striking change in form, except that the velum increased 

 in size, and the auditory vesicle appeared, containing several 

 otoliths, which kept up a rapid motion. But still the gills 

 and heart were wanting. Of its further early history we 

 know but little, except that it becomes fastened to some 

 rock and is incapable of motion. The oyster is said, by the 

 appearance of its shell, to be three years in attaining its full 

 growth, but this statement needs confirmation. M. Gerbe 

 has during the past year, according to La Revue Scientiftque, 

 cleared up some obscure points in the development of oys- 

 ters, but what they are is not stated. 



The development of a gigantic cuttle-fish, of an unknown 

 species, has been worked out by Grenacher. The mass of 

 eggs was thirty inches long. After segmentation of the 

 yolk, unlike other cuttle-fishes known, the embryo assumes a 

 spherical form, with a band of cilia, and is thus like the cil- 

 iated embryos of certain lower mollusks. This spherical 

 stage is also remarkable for the early appearance of the 

 mantle, with the contractile pigment-cells (chromatophores). 

 The embryo soon elongates, the mantle grows, the eyes and 

 arms bud out, and the form of the adult is rapidly sketched 

 out. 



Professor Hyatt has continued his studies on the Ammon- 

 ites, havincr described new forms of Jurassic and cretaceous 

 Ammonites collected in South America by Professors J. Or- 

 ton and C. F. Hartt ; and in another paper remarks on two 

 new genera, Agassiceras and Oxynoticeras. In a memoir on 

 the " Biological Relations of the Jurassic Ammonites," in 

 course of preparation, but of which an abstract has been 

 published, he traces the history of the evolution of the order 



