DEVELOPMENT OF NEPHRIDIA OP' PHERETIMA 95 



from the hypothetical original condition of these nephridia. 

 The development of secondary pharyngeal nephridia as distal 

 buds on the pharyngeal ducts is remarkable. 



11. Material and Technique. 



The material for this work consisted of cocoons of Phere- 

 tima containing embryos of various ages. In the Kew 

 Gardens, where I got my supply of these worms from, they 

 are found along with two or three other genera in the soil of 

 the Lily House, and, if the cocoons were collected from that 

 soil, it would be difticult to distinguish the cocoons of one genus 

 from another. Accordingly, to be quite sure of the specific 

 identity of my material, I tried the isolation and culture 

 method, which I briefly describe below. 



I took common garden soil and sterilized it for two or three 

 hours to kill all organisms in it, specially the cocoons of other 

 worms, eggs of insects, &c. This earth was mixed with sand, 

 and finally I added to this mixture a quantity of decaying leaves 

 which had also been previously sterilized. Four garden pots, 

 the bottom holes of which were closed with corks, were filled 

 with the sterilized soil and about fifteen worms of this species 

 of Pheretima were kept in each pot. These pots were kept 

 in a hot-house with an average temperature of 60° F. ; the 

 earth in the pots was kept moist and sterilized decaying leaves 

 were added from time to time. After the first two months 

 I was able to get cocoons in this way almost throughout 

 the year, and was always sure that the cocoons were of Phere- 

 tima alone and of no other worm. 



Various methods were tried to sift out the cocoons from the 

 earth, but the least troublesome, and therefore the best, is to 

 put a heap of earth in a fine sieve and to stir the earth while 

 keeping the sieve in a bucket of water. The earth passes 

 through the sieve and settles down at the bottom of the bucket, 

 while the cocoons are left in the sieve along with the large 

 pebbles and pieces of stone. The cocoons can be easily found 

 and picked up with a wet paint-brush. 



