1882.] Zoology. 911 



Early Stages of the Clam.— In the report of J. B. Ferguson, 

 Commissioner of Fisheries of Maryland, Mr. Ryder records his 

 observations on the early stages of the clam {Mya arenarid). The 

 -spawning period of this mollusk lasts from the ioth of September 

 to about the middle of October, or for about forty days. The 

 sex of the adults, in a spawning condition may be ascertained by 

 opening the shell carefully and removing a small portion of the 

 richly colored yellow body-mass with a knife, scissors or forceps. 

 These fragments traced out in a watch-glass with a few drops of 

 sea water, allow a milky fluid to escape. Under a magnifying 

 power of four or five times, the eggs of the female are visible in 

 this milky fluid as verv minute white points of nearly uniform 

 size, very nearly I -500th of an inch in diameter. The male cells 

 or spermatozoa are visible under a power of 250 diameters. Mr. 

 Ryder finds it possible after a little experience to observe with 

 the naked eye the differences between the male fluid and the 

 eggs. In two or three hours after artificial impregnation, i.e. by 

 pouring water containing the male cells over the eggs, develop- 

 ment begins. The changes which occur in the egg succeed each 

 other with considerable rapidity, and, as in the development of 

 the oyster, there are very well marked periods of active change 

 of form which alternate with periods of repose, while there is a 

 lalateral symmetry which is just as well marked as in the oyster 

 and unio. The development was followed as far as the forma- 

 tion of a gastrula, the process of which is the same as that of 

 the oyster, and in a general way the process of segmentation of 

 the egg of the clam appears to resemble, in its earliest stages, at 

 least, the same process in Anodonta, as described by Flemming 



Anatomy of the Ophiurid^.— Extensive observations upon 

 the Ophiuridae, carried on by M. Apostolides, at the laboratories 

 of Ranyuls and Roscoff, add considerably to our knowledge of 

 the anatomy of that interesting group. The mouth does not open 

 directly into the intestine, but into an cesophagus, provided with 

 a sphincter, by which it can be opened or closed at the will of 

 the animal. The so-called heart is in no sense a center of circu- 

 lation, but is a crlandular organ with an excretory canal. The vas- 

 cular apparatus consists simply of a system of lacunary spaces. 

 The body-cavity being completely closed, a perivisceral nutritive 

 fluid circulates within it. 



The genital clefts give access to ample closed sacs, carrying 

 upon their exterior surface the gen : prmcipally 



for respiration. The animal opens the clefts by the movement of its 

 arms or of the muscles around the mouth, and the sacs are then 

 filled by the action of the vibratory cilia of the inner layer. I his 

 takes place slowly, and when it is accomplished, the creature 

 ceases to move and the sacs drive out the water by their own 

 elasticity. This movement of the respiratory sacs is believed to 

 serve not only the purpose of permitting a gaseous exchange 



