318 Miscellaneous, 



to fully regain its activity, put out a pseudopod and moved in the 

 field, leaving behind it a group of the particles or granules. Only 

 for a little while, however, did it move ; in a few mom-ents it lost 

 its animation, seemed to become transparent, and at last faded into 

 one of those disks which seem to be merely the shells of once active 

 forms. I did not see it move again. 



This observation was carried on continuously during two hours 

 and a half, and every stage watched most closely. I was at a loss 

 what to call it, if not a clear case of conjugation and separation. 



The most convincing proof to my mind that this was a proceeding 

 which was for a purpose was given when, two nights after, this 

 slide, which was laid carefully aside for future examination, was 

 found to be full of young AmoehcB. They literally swarmed ; I 

 counted in the field at one time twenty-four of uniform size, while 

 I have no hesitation in saying that there were between one and two 

 hundred in the slide, which had before held but two. The worn- 

 out disk was recognized, and also what seemed to be the remains of 

 the larger Amoeba. — Proc. Acad. Nat. Sci. PliUad., Oct. 26, 1886, 

 p. 346. 



On the Byssal Organ of the Lamellibranchiata. 

 By M. Ltjdwig Eeichel. 



My researches upon the byssal organ have led me to the following 

 results, which differ from previous statements. 



From the observations of Reaumur and A. Miiller it is generally 

 regarded as proved that bivalve MoUusca which have once been 

 attached by a byssus are thereby prevented from changing their 

 place throughout their lives, unless they are torn away accidentally 

 by external force. The animals can, however, temporarily regain 

 their power of free movement, although not by tearing or separating 

 the byssus-threads as the two naturalists referred to thought possible, 

 but by throwing off the whole of the byssus, i. e. with stem and 

 root, when the organ is replaced by a new formation. This casting 

 of the byssus is a process exactly analogous to the change of skin 

 in the Arthropoda. In Dreissena ]}olymo72yha such a change of the 

 byssus takes place regularly at the commencement of the cold season. 

 In summer the animals are seated close to the surface of the water, 

 so that they are easily reached by the hand from the bank ; towards 

 the end of autumn, however, they retire into the deep water, leaving 

 their byssus behind them. 



As regards the formation of the byssus, it is almost universally 

 regarded as the secretion of special glands. I cannot adopt this 

 opinion, any more than that supported by von IN^athusius-Konigsborn, 

 that the byssus grows forth out of the tissues of the body of the 

 animal. The byssus rather originates as a cuticular formation, the 

 stem with the roots in the byssal cavity and the threads in the 

 pedal groove. Thus in those Lamellibranchiata which are provided 

 with a byssus the underside of the foot is traversed by a rather 

 deep longitudinal groove, which opens at the base of the foot into 

 a cavity, the so-called byssal cavity. In the opinion of those who 

 adopt the theory of secretion the foot and the walls of the byssal 



