H. M. FucHS 263 



in the investigation, namely, Ascidia mentula and Phallusia mamillata. 

 Besides these forms, four species of Echinoids — Strong ylocentrotus 

 lividus, Sphaerechinus granuhiris, Echinus microtuherculatus, and Arhacia 

 pustulosa — were made use of, together with one Asteroid, Asterias 

 glacialis. The procedure in obtaining the eggs and sperm of the sea- 

 urchins was this. Each individual was washed under a stream of fresh- 

 water to destroy any adherent spermatozoa, after which it was opened 

 by an equatorial cut. The aboral half was then reversed over a dish of 

 sea-water, so that the genital pores just dipped beneath the surface. If 

 the animal was mature, large quantities of eggs or sperm as the case 

 might be were shed into the dish of water, with very little admixture of 

 body cavity fluid'. The eggs of Asterias were obtained by cutting open 

 the body wall, after the animal had been washed in fi-esh-water, and 

 removing portions of the ovary. These were placed in sea-water, which 

 was presently filtered through bolting silk to strain off the pieces of 

 ovarian tissue from the eggs. 



The efficacy of these precautions was tested in every case by keeping 

 a sample of eggs separate, to which no sperm had been added. In no 

 experiment recorded here did a single egg in the control segment. 



By " egg-extract " is meant a suspension of crushed eggs in sea- 

 water. The eggs were crushed between two sterilized glass plates and 

 the substance so obtained washed off the glass into sea-water. By this 

 means a veiy finely divided suspension can be made, and presumably 

 soluble substances present in the eggs go into solution in the sea-water. 

 The suspension was examined after having been made up, to be certain 

 that no uncrushed eggs were lying in it, the subsequent fertilization of 

 which would destroy the value of the percentages. Throughout the 

 work the egg-extract was made up of more or less the same concentra- 

 tion, although it is impossible to make up two samples of absolutely 

 identical strength. For every 12 cc. of suspension, two drops of eggs 

 were crushed between the plates and then added to the water. 



" Ovary-extract " of Ciona was made up in the same way as the egg- 

 extract. In this case special precautions are necessary that none of the 

 spermatozoa from the testis have been removed with the ovary. To 

 check this possible source of error, unfertilized eggs from another 

 individual were in each case left lying in a sample of the ovary extract 

 and afterwards examined to see that none had segmented. 



"Egg-water"isused to designate sea-water in which eggs have been 

 lying for a longer or shorter interval. 



1 I am indebted to Dr Otto Koehler for bringing this method to my notice. 



