396 iriLSON. 



EXPLANATION OF PLATE XX. 

 ( Tt'dtinia Bi-ucei.) 



Fig. 67. Spicules: a, slightly bent strongyloxea ; /', oxea; c, tylote. («! 1^55 

 mm.) 



Fig. 68. Surface view, showing orifices intermediate in size between pores and 

 oscula. X 8. 



Fig. 69. Section showing bodies g, probably young gemmules, imbedded in 

 mesoderm. X goo. 



Fig. 70. Section : adult tissue with part of mature gemmule and a young gem- 

 mule. D.4. 



Fig. 71. Section: mature gemmule with surrounding tissue. A. 4. 



Fig. 72. Section through gemmule beginning to " segment." C.4. 



Fig. 73. Part of section through gemmule, completely broken up into masses. 

 D.4. 



Fig. 74. Part of section through gemmule near the close of "segmenta- 

 tion." C.4. 



Fig. 76. Section through embryo — columnar ectoderm entirely covers em- 

 bryo. A.4. 



Fig. 77. Longitudinal section through unpigmented pole of embryo — cells at 

 this pole still columnar. D.4. 



