283 



What is remarkable, too, the pseudopodia, as frequent and careful 

 observations have led him to determine, invariably alternate with the 

 cells of the exterior layer; that is, they are prolongations of the in- 

 tercellular amorphous substance of the body. This fact would seem 

 to add to the proof that the so-caUed vacuoles are really cells ; other- 

 wise it would be hardly credible that simple vacuoles, which come and 

 go in an amorphous substance, should always alternate with the pseu- 

 dopodia. 



Sometimes, a pseudopod moves very rapidly, especially when it has 

 seized upon some victim, for then it retracts with a sudden jerk, and 

 draws the prey close to the body, which finally engulfs it, in the same 

 manner as does Amceba. The pseudopodia exhibit an adhesive power, 

 which is remarkable when we consider the size of the animals which 

 are sometimes drawn in by them, and, in this respect, remind one of 

 the " adhesive vesicles" in the anchors of Lucernarise, which hold fast 

 to bodies with the greatest tenacity, and, to all appearances, by simple 

 contact, just as glue and mucus adhere to anything which touches 

 them. (See my paper on " Lucernaria, the Canotype of Acalephse." 

 Proc. Bost. Soc. Nat. Hist, Vol. ix., 1862, p. 52 ; and also, reprinted, 

 " with additions and notes," in SilUman's American Journal of Science, 

 for May, 1863, p. 352.) In a Difflugia (very near D. proteiformis), 

 Prof Clark had observed that whenever the pseudopodia contract, 

 they invariably become strongly wrinkled transversely ; and, as he 

 could not detect the least trace of an envelope, or wall-like layer, on 

 this part of the body, he believed that the wrinkling is peculiar to the 

 substance of the pseudopodia.* 



* In this connection, I will take the opportunity to assert, that, from a number 

 of observations on various animals, I have been led to the conclusion that allvibra- 

 tile cilia originate in the amorphous intercellular substance. In no instance have I 

 ever seen vibratile cilia forming direct prolongations of ct41s: but invariably I find 

 their bases imbedded in the intercellular cytoblastema. They may seem to be pro- 

 longed from the underlying cells, but, on the contrary, as I have particularly satis- 

 fled myself, in regard to the brauchise of the oyster, Ostrea Vii-giniana, they are 

 based in the cytoblastema, which extends in a thin stratum over the outer ends of 

 the cells. In other instances, they alternate with the cells, projecting in rows 

 between them, and forming, as it were, a bristling corona to each cell, as I 

 have seen in the epithelium of the intestine of the young snapping- turtle, 

 Chelydra serpentina. In the latter instance, when the cells are loosed from 

 the intestine, they carry the overlying cytoblastema with them, and conse- 

 quently, also, the vibratile cilia, which then falsely appear like appendages 

 of the cells themselves. The nettling cells, cnida:, of Polypi and Acalephje origin- 

 ate in the same substance, the intercellular cytoblastema, as do vibratile cilia. 

 They have been supposed to develop loithin the cells of the layer in which they are 

 situated; but this is not true. Oftentimes, when cnidse are removed from their ba- 

 sis by pressure, tliey drag along with them a portion of the cytoblastema, which 

 encloses them like a transparent envelope, and has the appearance of a cell. Some- 

 times three or four cnidse are pressed out together, and, being covered by the accom- 

 panying cytoblastema, they present the deceptive appearance of several cnida?, in 

 one cell. 

 There are four periods in the history of Cnida . Wegner ( Wiegm. Archiv, 1853) 



