CHAPTER X1I1 

 EOTIFEKA 



Classification a d 'opted 



1. Floscularidea. 4. Asplanchnidea. 



2. Melicertidea. 5. Scirtopoda. 



3. Bdelloida. 6. Ploima. 



THE liotifera are a puzzling group of minute animals about whose 

 affinities most contrary views have been held. The extremely small 

 size of the adult, and consequently of the egg, has made the investi- 

 gation of the development extremely difficult, but within compara- 

 tively recent times Zelinka (1892) has published a most satisfactory 

 account of the development of Callidina russeola, and this we shall 

 accordingly select as type. Jennings (1895) traced the cell-lineage 

 of the egg of Asplanchna Herricki for a few generations, but, as he 

 did not correlate the regions of the cellular embryo to the organs of 

 the adult which resulted therefrom, his work is of no value for us. 



CALLIDINA IIUSSEOLA 



Callidina russeola belongs to the division of Eotifera known as 

 Bdelloida, in which there is an eversible proboscis in the mid-dorsal 

 line, and in which the ciliated organ is represented by two semi- 

 circular retractile hoops placed at the sides of the proboscis, and in 

 which the body ends in a " foot " terminating in a pair of forceps. 

 Callidina lays what is, for its size, a comparatively large egg. The 

 egg-case measures -1 mm. in length, and the whole of the development 

 takes place after laying ; a period of seventeen days is required 

 before the completed embryo escapes from the egg-case. Callidina 

 is an inhabitant of the drops of water which cling to the thickly 

 matted leaves of moss plants, and the eggs can be found by rinsing 

 the moss in water and examining the washed-out rubbish under a 

 low power. It is, however, better to catch adult specimens of 

 Callidina and keep them in clean watch-glasses until they lay 

 their eggs. 



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