88 HUBERT LYMAN CLARK ON SYNAPTA VIVIPARA. 



Fig. 71. Cross-section of the terminus of a stone-canal with two openings, to show the uppermost opening. 500x. 



Fig. 72. Cross-section from the same series, two sections lower down. 500x. 



Fig. 73. Cross-section of the same series, two sections further down, to show the second opening. 500x. 



Fig. 74. Cross-section of a stone-canal of an adult, taken through the madrepore to show the openings. 225x. 



Fig. 75. Longitudinal section of nerve-ring of an adult (transverse section of the animal), to show the nerve-band to the 

 mouth and oesophagus in cross-section. 200x. 



Fig. 76. Transverse section of nerve-ring (longitudinal section of animal), to show the same nerve in sagittal section. 

 200x. 



Fig. 77. Longitudinal section of nerve-ring and transverse section of tentacle-nerve, to show the position of the eyes. 

 120 x. 



Fig. 78. Cross-section of nerve-ring and one of the eyes, to show their relative position. 225x. 



Fig. 79. Cross-section of the tip of one of the eyes, to show the vacuolated structure of the mesenchymatous covering as 

 well as of the polygonal neive-cells. 950x. 



Fig. 80. Sagittal section of one of the eyes, to show the shape and structure of the nerve-cells. 950x. 



Fig. 81. Cross-section of an otocyst and its single vesiculated cell from a pentactula. 500x. 



Fig. 82. Cross-section of the otocysts and a part of the radial nerve from a twelve-tentacled young five mm. long. 

 500x. 



Fig. 83. Cross-section of an otocyst of an adult, showing the single vesiculated cell-'within. 500x. 



Fig. 84. Cross-section of a sense-papilla in the ectoderm of an adult, to show its structure and nerve connections, ga, 



ganglion ; n, nerve running to radial nerve. 500x. 



PLATE 15. 



Fig. 85. Transverse section of an old pentactula, to show the formation of the five accessory tentacles and the oto- 

 cysts ; the secondary outgrowths of the left dorsal and mid-ventral radii have not developed at all as yet. The section is 

 slightly oblique, more posterior on the left than on the right. 225x. 



Fig. 86. Transverse section of an old ten-tentacled stage, to show position of the eleventh and twelfth tentacles. The 

 section is somewhat oblique, more posterior on the right than on the left. 120x. 



Fig. 87. Longitudinal section of the anterior end of a pentactula ; on the left through a radius ; on the right a little to 

 one side of a radius. /, indicates the place of fusion between the oesophagus' and roof of the atrium. 225x. 



Fig. 88. Another section of the same series; on the right, through an interradius, just touching on the side of the 

 Polian vesicle ; on the left a little to one side of an interradius. /, indicates the fusion of the oesophagus with the roof of 

 the atrium. 225x. 



Fig. 89. Longitudinal section of a ten-tentacled young, to show position of the various organs. 65x. 



Fig. 90. Longitudinal section of an adult through one of the tentacles, to show the position of the various organs. 35x. 



Fig. 91. Longitudinal section of an adult through a radius, to show position of the organs. 35x. 



Fig. 92. Adult laid open in right dorsal radius, to show position of the organs and especially the blood-vessels on 

 digestive tract. Nat. size. 



Fig. 93. Larval monstrosity, a double embryo. 225x. , 



Fig. 94. Cross-section of longitudinal muscle of adult at the point of juncture with the calcareous- ring. 65x. 



Fig. 95. Cross-section of same muscle, lower down. 65x. 



Fig. 96. Cross-section of same muscle, lower down. 65x. 



Fig. 97. Cross-section of same muscle, lower down. 66x. 



Fig. 98. Cross-section of longitudinal muscle of a smaller adult, somewhat anterior to the middle of the body. 200x. 



Fig. 99. Cross-section of a longitudinal muscle in the middle of the body. 80x. 



Fig. 100. Cross-section of a longitudinal muscle at extreme posterior end'of the body. 200x. 



Printed, January, 1898. 



