376 



GRACE MEDES 



and is the most usual type. It is very much simpHfied in out- 

 line, thickened in every portion of the skeleton, with only slight 

 traces remaining of the lattice-formation in the anal arms, and 

 with a reduction in the number of spines and processes of the 



Fig. 83 9/, 48 hrs. All the principal parts heavier. Precocious fusion of 

 the arms. Lack of processes. Reduction in size. 



Fig. 84 9g, 48 hrs. Same chracaters except that here the lateral connec- 

 tives and the body-rods have not fused. Specimen very symmetrical. 



Fig. 85 9/, 72 hrs. Usual type. Skeleton thickened, simplified in structure. 

 Slight traces of lattice-formation. Reduction in the number of spines and 

 processes. Highly symmetrical. 



Fig. 86 9/, 72 hrs. Skeleton heavier than in figure 85, the two halves 

 unfused. 



Fig. 87 9/, 72 hrs. Two portions of the skeleton unfused. Dorso-ventral 

 connectives (?) turned laterally, with oral arms (?) turned posteriorwards. 



body-rods, yet it shows no indication of lack of symmetry. The 

 tendency toward irregularity of structure under the various 

 other experimental conditions described above is entirely lack- 

 ing here, and a comparison of the measurements taken of the 

 two sides of the body in these cultures shows quite as little 



