A ROTIFER PARASITIC IN TEiE EGG OF THE WATER-SNAIL. 485- 



poor things, looking quite starved, and clinging to the inside of 

 the egg-shell instead of, as earlier, floating in the contents ;. 

 evidently there is nothing left to feed upon. 



From now to the thirteenth day, when these observations 

 were brought to a close, these four remained, and were- 

 practically dead, although a little movement could be seen. 



Now the question arises : What has become of the parent and 

 young ones which left this egg 1 To answer this question 1 must 

 refer to Nos. 2, 3, 4 and 5 on my diagram. No. 2 was not 

 infested until the fourth day. No. 3 on the third. No. 4 on. 

 the second. No. 5 on the third day. 



It is safe to assume that the Proales which left No. 1 were- 

 the same which reached the healthy Nos. 2, 3, 4 and 5. The 

 course these ran was much the same as No. 1, with slight 

 variations in number of eggs, viz. from seven to thirteen. I 

 have seen some of the snail's-eggs absolutely stuffed full, 

 counting over thirty, in all stages of development, but in those 

 cases there were three full-grown animals, who were no doubt 

 the parents. 



As they leave the snail's egg they seem to flounder aimlessly 

 about in the jelly-mass, but no doubt find comfortable quarters- 

 and good feeding ultimately. I observed, while mounting, that 

 they were not at all " at home " wdiile out in the open water. 

 This is a true parasite, spending the whole of its life inside the 

 snail's egg, Avith the exception of the time taken in scrambling^ 

 from one egg to another. 



It must not be supposed they all deposit their eggs and 

 depart, for they must die somewhere. No. 6, although a strong- 

 looking Rotifer, died on the third day, leaving nine eggs behind, 

 and her remains were devoured, along with that of the embryo 

 snail, by her progeny, the finishing touch being put by the 

 appearance of a number of septic organisms on the sixth day. 



The boring of the hole in the snail's egg-shell is not an easy 

 matter, for it is very tough and resistant. So much so, that 

 it was very difficult to break the shell (to get out the Proales) ; 

 they persisted in slipping from under the needles. I found the 

 best plan was to get the egg in the compressor, and gently screw 

 down ; it would then burst, and the Rotifers flow out. To show 

 the toughness of the shell, the point of breakage was distinctly 

 felt by the hands holding the compressor. The weed most 



