556 DR. L. ORLEY. 



presumably secreted by the clitellum. The cocoons of the 

 Criodrilidse, however, are spindle-shaped, parchment like struc- 

 tures with a colour that changes ; they are about 5 cm. in 

 length, rapidly diminishing towards each end. One end, 

 drawn out into strongly fibrous threads, serves for attachment 

 to the roots, or more rarely to the leaves and branches of 

 water plants ; the other end truncated, with a dentate edge, 

 allows the embryos to escape. As is the form, so also is the 

 colour different. The perfectly newly laid cocoons are nearly 

 transparent, horny yellow in colour, but after a time they 

 become darker, and towards the time of hatching of the 

 embryos they are blackish in colour. This change in colour, 

 which reminds me of the egg cases of Shark embryos,^ may 

 here too be traced to chemical changes. 



The substance of the egg cases is not wholly chitinous ; at 

 any rate a large portion is dissolved in caustic potash ; on the 

 contrary, a sort of coagulated yolk and mucus take a large 

 share in their constitution. The substance itself is very easily 

 wetted, so that liquids and gases can diffuse through it. 



The inside is filled with a fluid albuminous substance, allied 

 in density to white of egg ; in this from eight to twenty eggs 

 are embedded, and in it are found the remains of the sub- 

 stance of the spermatophores as well as innumerable sperma- 

 tozoa, which are to be met with especially round the develop, 

 ing eggs; their appearance is reproduced in fig. 8, PI. XXXVTII. 

 The number of eggs is very variable; usually only one third 

 of the fertilised eggs develop ; the largest number of embryos 

 in a cocoon was eight, the smallest two. 



The structure of these egg cases is especially well shown, if 

 freshly laid eggs, preserved in alcohol, are placed in water in 

 order that they may swell up. When such cocoons are care- 

 fully examined the swollen part is found to be banded ; these 

 bands appear to correspond with the somites of the anterior 

 part of the body. This correspondence, as well as the fibrous 

 structure of the outermost layer (fig. 2) and the remains of the 

 ^ L. Orley, "Zur Physiol, der liaiembryoneii," ' Termeszet. fiizetek,' ix, 

 1885, Buda-restb. 



