4 ART. 17. — ^^ YAÏSU. 



live hours in sea-water, were almost as lively as when just taken 

 out of the male. 



In order to obtain one particulnr stage for some time five 

 or six lots of eggs were kept in salt-cellars and fertilized in 

 succession at regular intervals of, say, fifteen minutes, w^ith a 

 small drop of sperm-water prepared as described. When the 

 desired stage was reached, several eggs were taken out on a slide 

 with very little w^ater, so that they w'ere somewhat flattened. 

 In case the slide has even a little grease on it, the water stands 

 up as a drop and does not spread. This difficulty was easily 

 removed by smearing with a little saliva and afterwards washing 

 it off w^ith a brush. For operation Jaeger's straight keratomy 

 knife was used w^ith profit. Soon after the cut was made under 

 a dissecting microscope, more water was quickly added. Then 

 the angle of the section and the size of the fragments were 

 recorded. Each fragment was allowed to develop separately in 

 an embryological salt-cellar (capacity 20 c.c.) containing fresh sea- 

 water. 



Not only the early cleavage stages and the resulting pilidia 

 of the eggs operated on, but also their intermediate mode of 

 development was examined several times, since it is often the 

 case that well started egg-fragments, afterward take an abnormal 

 course which leads to abnormal pilidia. It was found sometimes, 

 if not always, necessary to move round the egg-fragments at the 

 blastula stage by means of a gentle jet of water from a fine 

 pipette, since if this precaution is neglected they may be stuck 

 to the bottom with their own gelatinous secretions, which afford 

 bacteria an excellent medium to grow in. Embryos, which survive 

 the early blastula stage, are very tenaceous of life and live in a 

 healthy condition for several days in a salt-cellar, the wat^' in 



