79 267 



the number of flame cells vary from 20 — ^40, the contractile vesicle is large; Irophi 

 are constructed as in the next form but somewhat smaller (95 — 1.35/* long). Length 

 of entire animal 500 — 1200/(. 



In B. the corona is oval ; the flame cells 40 — 60. The contractile vesicle small ; 

 trophi strong 130 — 200,« mainly 150 — 170/», enclosing, when closed, an area which 

 is. not oval, but widest in its distal third, with prominent tooth projecting inward, 

 delicate lamellate teeth near the tips, and the two rami interlocking, when closed, 

 by means of one bifid and one pointed tip. Length 1000 to 1800 /<. 



In C the body is very broadly saccate to broadly campanulate with very heavy 

 walls and muscles strongly flattened dorso-ventrally, never with humps; corona 

 oval and verj' broad, its breath frequentlj^ equalling the length of the animal; coro- 

 nal disc concave, instead of convex; flame cells 80 — 115, contractile vesicle small; 

 trophi 300 — 340 fi, very large, enclosing a narrowly oval area; inner teeth compara- 

 tively less prominent than in preceding types, set at an acute angle with the ramus, 

 and more firmly fused with it than in the preceding types; lamellate teeth near tips 

 of rami much developed and meeting with cutting edges in middle line; lips of rami 

 not interlocking, but shearing past each other when closed. Length of entire animal 

 approximately 1800 to 2500 /t. 



It was further shown that intermediate stages were commonly rare, and that 

 the three forms were standing sharply against each other; they were not all to be 

 found in the same sample, and all three forms were not necessarily developed in 

 all the small localities, where the species was examined. 



There are also other differences to point out in the three forms, especially with 

 regard to propagation; the saccate form which most probably is the only one which 

 develops from the resting egg, is usually crowded with embryos, nine or more; the 

 humped form as a rule contains only one single young one and the campanulate 

 form contains a few; by means of degeneration in cultures the saccate form may 

 derive from the humped one, but this is an exception. The campanulate forms make 

 their appearance within at most a week. Sometimes a single individual, either young 

 or fully developed, would first be discovered. In every instance the sudden appearance 

 of the campanulate form was followed by its very rapid multiplication, coincident 

 with a still more rapid diminution in numbers of the humped form. The latter were 

 eaten up by the former. Campanulate forms were also reared in the cultures by using 

 the young Moinas as food, and a pond was discovered where the natural appearance 

 of Moina caused an enormous production of campanulate forms, even directly from 

 saccate ones, without humped ones as an intermediate stage. The entire population 

 of a teeming Asplanchna-^onà readily changes from the saccate to the humped type 

 in one week; the saccate forms giving rise to the humped ones in the first genera- 

 tion, almost of the same size as the mothers. The next generation gives large-sized, 

 typical humped individuals; later on the campanulate form appear among them with 

 the utmost abruptness owing to canibalism. Between the alterations in the colonies, 

 when they pass from one form into another, transitional periods appear; in these 



