CELL DIVISION IN EGGS OF CREPIDULA. 526 



were placed. Sala (1893) and Zur Strassen (1898) found that the eggs of Ascari* 

 megalocephala might be caused to fuse together by cooling them to 3° to 4° C. 



My own work on the influence of altered temperature on the cleavage proc- 

 esses of Crepidula are limited to ten experiments, — nine on the effects of increased 

 and one on the effects of decreased temperature. At the time the experiments 

 were made the normal summer temperature of the sea water at Wood's Hole was 

 about 22° C. ; however the temperature of the water in the finger bowls in which 

 the eggs were developing normally, varied from 22° to 27 



In the experiments with increased temperature the eggs were taken from finest 

 bowls at room temperature, in which the thermometer registered from 22° to 

 27°, and were put into sea water varying in the different experiments from 33' 

 to 38° C. They were kept in the warm water from Y± hr. to 4 hrs.; some of tin 

 eggs were then fixed at once, while others were put back into the finger bowl 

 in water which varied with the room temperature from about 22° to 27°, where 

 they were left for periods of time varying from 3 hrs. to 15 hrs. The records 

 of each of the experiments are given in the catalogue at the end of this pa r. 



The eggs thus treated showed many notable chanp>s in structure— in< d 

 in no other experiments recorded in this paper were the modifications so great 

 and so interesting. That these modifications are not due merely to heat coagu- 

 lation is shown by the partial or complete recovery of the eggs when returned 

 to normal conditions. However owing to the relatively small number of experi- 

 ments, I have not been able to analyze these modifications as thoroughly as 

 could be wished. This I hope to do in a later paper, as I am now engaged in 



extending these experiments. 



In the experiments with altered temperature, as in all the others, the greatest 

 changes are produced when the eggs are in some phase of kinesis at the beginning 

 of the experiment, while stages of interkinesis arc affected relatively little. The 

 early stages, also, are more affected than the later ones. The most ge 

 results of increased temperature are: (1) Reduction of surface tension 

 consequent irregularities in the outlines of the eggs; owing to local reductions of 

 surface tension the type of polar-body formation or of cleavage may be greath 

 changed (figs. 94, 95). (2) Segregation of archiplasm (hyaloplasm and chro- 

 matic nuclear sap) into distinct areas, separate from the clearer plasma (enchy- 

 lema); withdrawal of the archiplasm of the astral radiations intc .the central 

 areas of the aster and into the division walls between cells (figs. 94-99). \6) i ro- 

 found changes in the orientation and structure of the mitotic figures; loss ot an 

 spindle fibers and centrosomes; scattering of chromosomes, which are oiten 

 thrown entirely outside the mitotic figures and even outside the cytoplasmic 

 — ^ a . *.-**,. (4) Formation of numerous karyomeres from these scattered 

 chromosomes; indeed by slight increase of temperature almost every enromo- 

 some may be caused to remain distinct from every other one, and to give nse w 



a separate chromosomal vesicle. 



Only one experiment was made on the effects of decreased temperature on 



d 



(figs. 97-99) 



