34 HARRIETT M. ALLYN. 



cleavage. The flow of cytoplasmic material in the egg keeps up 

 in one direction for a time, accompanied by a deepening con- 

 striction in the egg, until suddenly the direction of the flow 

 changes, or a new wave is set up, and all appearance of constric- 

 tion or cleavage is lost. Often the flow is set up in opposite 

 directions at once, and thus the constriction plane is simulated, 

 but one flow suddenly overcomes and obliterates the other. 

 The polar lobes also disappear. The amoeboid movements noted 

 in so many eggs are to be seen in Chcetoptents also, so markedly 

 that at one time successive camera drawings showed that the egg 

 actually moved along the slide for some little distance. Pseudo- 

 cleavage takes place to some extent, that is, cleavage of the 

 cytoplasm without cleavage of the nucleus. There is also indi- 

 cation of amitotic cleavage of nucleus and cytoplasm together. 

 As development proceeds the nucleus increases in size, and a mass- 

 ing of the cytoplasmic materials in different parts of the egg 

 can be seen. At ten or eleven hours the larvae are beginning 

 to swim, several hours later than fertilized eggs. The percent- 

 age of swimmers at 20-24 hours varies greatly. Usually the 

 larvae were not kept longer than that, but on one occasion they 

 were kept nearly 48 hours, and at the end of that time I find 

 that my notes record, "Full of very active swimmers, some even 

 having risen in the water, and all much resembling trochophores 

 in general appearance." Many larvae are able to swim in a 

 comparatively straight course, others spin round and round, 

 others do now one, now the other. There are many fusions 

 and some fragments, any of which may be ciliated. Some are 

 composed of a few pseudo-cells, but many are one-celled and also 

 uninucleate. Vacuoles are noticeable in or near the surface. 



Fixed Material. Eggs from Set B were fixed every five minutes 

 for the first two hours and fifteen minutes, and every half hour 

 thereafter to 19 hours 30 minutes, with a few more at five- 

 minute intervals during the period of chromatin distribution. 

 Eggs from Set A were fixed every half hour or less. 



The history of the development is in general as follows. 

 While the eggs are still in the potassium chloride solution the first 

 maturation division is carried through and the first polar body 

 extruded; the nucleus of the second polar body, if formed, is 



