INCLUSIONS IN EGG OF ECHINARACHNIUS 483 



stained with ordinary reagents, and to show the part played by 

 them in the processes of development initiated by fertilization. 



SUMMARY 



1. The cytoplasm of eggs of Echinarachnius parma when 

 fertiUzed by sperm of the same species shows no visible differ- 

 ences from that of eggs fertilized by Arbacia sperm. 



2. Fat drops occur in the unfertilized egg. These drops are 

 emulsified and the fine droplets of fat thus formed gradually 

 become used up or transformed during the early cleavage stages. 



3. Small spherical mitochondria are found scattered through- 

 out the cytoplasm and there is evidence to show that they are 

 the direct products of the fine fat droplets. 



4. The cytoplasm is packed with plates of nutritive material 

 which have some fatty component in their makeup. They are 

 probably yolk. They are in some cases closely associated with 

 mitochondria, and it is probable that the mitochondria are 

 instrumental in their synthesis. These plates gradually become 

 fewer in number and in the blastula the cytoplasm is quite 

 spongy and full of vacuoles once occupied by the plates. 



5. After certain fixatives, picro-acetic and sublimate-acetic, 

 large precipitations of colloidal material in the cytoplasm are 

 stainable with iron hematoxylin. Other fixing fluids preserve 

 them, but do not mordant them so that they actively take up 

 the stain. These precipitations are found in the unfertilized 

 egg when its cytoplasm is in a sol state. They cease being 

 formed as the cytoplasm becomes a gel during its preparation 

 for the first division. 



JOURNAL OF MOBPHOLOGT, VOL. 36, NO. 3 



