Ceiitrosonie in Enucleated Egg-Fragments. 30 1 



of appearance of the cytasters; in one case the cytasters \\ ill develop 

 throughout the fragment as in Fig. 6, while in the other one, 

 two or three cytasters will appear near the center. Suppose in 

 the latter case these cytasters grow to a considerable size, accom- 

 panied by the multiplication of the centrioles, then we shall have 

 a condition somewhat similar to that shown in Fig. 7 (in this 

 case it should be mentioned only one cytaster has been formed). 

 Meanwhile the rays degenerate, leaving radiating line of yolk 

 granules behind. The granules are pushed out as the centrosome 

 grows. In case two or three cytasters appear they finally fuse 

 together, giving rise to a huge central space. The yolk granules 

 found as islands in the clear area may be the remnant of the 

 interastral spaces. In fact, in some cases the yolk island is con- 

 nected by a narrow bridge with the peripheral yolk layer. Then 

 most of the centrioles move out toward the periphery of the clear 

 space. Each centriole acquires a daughter ray system around it. 

 The condition shown in Fig. 8 is thus reached. (Morgan, '99, 

 PI.' 10, Figs. 67, 68, 70 and 60B.) 



B. Etjucleated Fragmejits Treated with the CaCU Solutiony 



T ime-Sterilization. 



To test whether the formation of the cytasters in the enucleated 

 fragments be due to the action of the CaCl. solution or to the 

 heat-sterilized sea-water I made a few experiments using sea- 

 water kept for two days, the precautions and subsequent treat- 

 ment being the same as Experiment A. 



The cytasters appeared exactly in the same way as the experi- 

 ments in which the heat-sterilized sea-water was used. Two 

 fragments are shown in Fig. 12a and 12b. One piece was cut 

 into sections. The cytological characters of the cytasters were 

 similar to those of Fig. 8. 



From this experiment it will be seen that the formation of the 

 cytaster is entirely due to*the action of CaClj. 



C. Enucleated Fragments Treated ivith the MgCU Solution, 



Heat-Sterilization. 



An enucleated fragment was put in the MgCL solution used 

 by Morgan (3.5 per cent of MgCl, in the sterilized sea-water). 

 When I examined this frao-ment after half an hour a clear area 



