150 John H. Geroüld, 



in the late afternoon, males of Ph. vulgare in which the nephridia, 

 full of sperm and enormously elongated, could be distinguished 

 through the translucent walls of the body. The nephridia of females 

 in this condition, however, are rarely visible through the bodj^-wall. 



Rearing of the Larvae. When the trochophores have 

 risen to the surface of the aquarium they should be transferred to 

 a crystallizing dish of fresh sea-water, so that they may descend 

 to a clean bottom after metamorphosis. Thereafter it is only ne- 

 cessary to siphon or pour off the water once or twice each day, 

 and to keep the dishes covered. The use of Ulva and other algae, 

 as ordinarily employed, is not to be recommended, for they serve 

 only to foul the bottom of the aquarium, which should be kept 

 scrupulously clean. The young worms get sufficient oxygen from 

 the large volume of fresh sea-water in which they should be kept. 

 Thus, by transferring the larvae occasionally to clean dishes, they 

 will live for a month or more in excellent condition. By the end 

 of the second week the yolk supplies are nearly exhausted, and 

 growth would probably be facilitated if the larvae could be reared 

 thereafter in muddy sand, but I have never succeeded in finding 

 again specimens that I had placed under such conditions. 



Fixing Fluids. Lang's formula of three parts of ö"/,. solution 

 of corrosive sublimate in sea-water, plus one part of glacial acetic 

 acid, was used with excellent results in preparing eggs for the 

 study of maturation and fertilization. Hermann's platino-aceto-osmic 

 mixture w^as also found useful, though not so reliable as the aceto- 

 sublimate mixture. 



For the study of cleavage, eggs were fixed in the following 

 solutions: picro-nitric, Perenti's, aceto-sublimate, Flemming's, and 

 saturated solution of corrosive sublimate in sea-water. The diffi- 

 culty of staining after the use of any of these reagents will be 

 discussed below. 



In studying the trochophores and larvae, aceto-sublimate, Her- 

 mann's platino-aceto-osmic, and Perenyj's mixtures gave excellent 

 results. Saturated solution of corrosive sublimate, used without 

 acetic acid, is not to be recommended. In order to fix the larvae 

 in extended condition, it is necessary to use the fixing fluid hot, or 

 to stupify the animals with some anaesthetic. I have used chloral 

 hydrate for this purpose with good results. 



Staining. -No satisfactory nuclear stain for the early stages 

 of cleavage was obtained after any of the fixing fluids mentioned 



