1921] NATURAL SCIENCES OF PHILADELPHIA 131 



distinct and still. The most interesting fact about that change in 

 shape is perhaps the pointed extremity which never exists in the 

 resting stage, and certainly seems an adaptation for swimming. 



Plate VI, fig. 30 illustrates a case of division, nearly completed, 

 such as I met with on the 8th of February. Very likely the process 

 had been the same as that described in the previous chapter, for 

 Salpingoeca polygonatunu The new Flagellate, ovoid in shape, is 

 seen about to draw its flagellum from the shell it has just left, and 

 beginning to glide down towards the supporting Alga. It is seen 

 about ^ of a minute later, nearly touching the ground but with 

 its flagellum still attached to the border of the cup (Plate VI, fig. 31) ; 

 one minute more, and the flagellum was free, pointing straight up- 

 wards, the protoplasmic collar had begun to develop, and the in- 

 ferior extremity had become pointed. Very likely the rudiments 

 of a new capsule were already beginning to appear; but at that 

 very moment, the supporting Nostoc passed into some rubbish and 

 was lost to sight. Other specimens, however, were found that 

 same day and the next, at the stage just described (Plate VI, fig, 32), 

 and they allowed of further observations :* 



Immediately after fixation, the little body takes the form of a 

 long top, with a distinct plasmatic collar, in which food particles 

 are already caught; but the characteristic posterior point immedi- 

 ately changes into a very fine thread, and as the body gets higher 

 and higher, leaving the ground behind, the thread gets longer, being 

 just sufficient to prevent the escape of the Flagellate, but certainly 

 unable to keep it upright. The body, in fact, is kept upright by 

 a very thin envelope, which has already formed, the appearance 

 being that of an egg in its cup (in Fig. 33, Plate VI, dotted lines 

 indicate the rudiments of the shell). The new envelope is so thin, 

 that one hardly can detect it, like two fine fines left and right of 

 the point of fixation, and which diverge more and more to meet 

 the body in its most swollen portion. The animalcule, in fact, 

 rose while propping itself against the very borders of the partly 

 constructed cell; but after a normal height has been reached the 

 body ceases to get higher, the posterior thread disappears, the ani- 

 malcule swells and moulds its body into the very form the shell 

 will invest afterwards, and deposits all over its own surface a very 

 thin pellicula, then retracts when the pellicula has become hard. 



'Several of these specimens seemed from their particularly large size to rep- 

 resent adults, which had left their shell without previously dividing. 



