EMBRYOLOGY OF TEREBRATULINA. 263 



PLATE IX. 



The figures of embryos npon this plate as follows : 78, 79, 80, 81, 82, 83, 85, 86, 87, 88, 89, 90, 91, 92, 93 

 and 94 were drawn with a Wales J inch ; a few of them are shown less magnified on Plate VIII. 



Fig. 78. Free swimming embryo showing first trace of alimentary tract and peduncular segment. 



Fig. 79. Free swimming embryo showing deciduous setse projecting behind. This feature was only 

 observed in two instances. 



Fig. 80. Showing widening of thoracic segment, depression of cephalic segment, and first attachment of 

 caud.al segment. 



Fig. 81. Appearance of embryo Fig. 85 after having been crushed. The embryo shell, apparently corneous, 

 is split at the peduncul.ar end. The membrane representing the head and cephalic wall is bulged out, with 

 ruptures from which the celkdar contents of the body are escaping, and the deciduous setoe are separated from 

 their base of support. 



Fig. 82. First stage in which the mouth makes its appearance, and dorsal and ventral plates become dis- 

 tinctly marked. 



Fig. 88. Earliest stage in which definite internal structure was found. The peduncular segment character- 

 ized by thick walls is seen hanging in the thoracic or pallial cavity. 



Fig. 84. Highly magnified drawing of deciduous setas showing their barbed character. 



Fig. 85. Showing arrangement of deciduous setae, and contour of embryonic shell. 



Fig. 86. Another stage similar to that shown in Fig. 83. 



Fig. 87. Showing first bulging of thoracic ring and clear interspace within. This region is characterized 

 by large granules marking its wall, and in first losing its ciliary lining. The bulging probably indicates the 

 region of the larger or ventral valve. 



Fig. 88. A stage slightly advanced from Fig. 85, showing change in outline, the anterior margin strongly 

 ciliated. The deciduous setre were easily dislodged at this stage, and were often lost in examination. 



Fig. 89. A portion of shell of Fig. 88 crushed, showing by its fracture a harder consistency. 



Fig. 90. Stage showing for the first time a primary cirrus or tentacle upon each side of its head. 



Fig. 91. The same crushed, showing fracture of shell, and parts forced out by pressure. 



Fig. 92. Stage similar to Fig. 85. 



Fig. 93. A slightly advanced stage from Fig. 92, showing widening of anterior margin. 



Fig. 94. A stage slightly advanced from the preceding, with a definite structure showing in the anterior 

 portion of shell. 



Fig. 95. Adult characters now assumed, permanent setre now showing, and pallial coeca present. 



Fig. 96. The youngest stage met with in which adult characters were present. The permanent setae, 

 seven in number, project from the anterior margin. The peculiar scaled structure of the shell is just appear- 

 ing, and the primary pallial cceea are present. Within, the rounded stomach, and four tentacles are shown. 



Fig. 97. Head, tentacles and stomach from an advanced stage. Figured particularly to show contour of 

 parts about the head. 



Fig. 98. A stage consiilerably advanced from Fig. 96, showing subsequent widening of the anterior por- 

 tion of the dorsal and ventral plates. 



Fig. 99. A setigerous follicle with its seta. 



Fig. 100. a. b. One of the primary pallial coeca, showing appearance of fringing hairs, a. Showing the 

 position of hairs before being disturbed by a brush, and b, the same after having been brushed with a delicate 

 camel's hair pencil. These are from Fig. 105. 



, Fig. 101. A tentacle, or cirrus from Fig. 102, showing cavity within, and arrangement of calcareous parti- 

 cles, and relative size of cilia clothing it. 



Fig. 102. A considerably advanced stage drawn to show relations of embryonic area, which is shaded. 

 This portion corresponds to stage shown in Fig. 94. 



Figs. 103, 104. Showing .appearance of fringing hairs bordering pallial ececa. 



Fig. 105. Advanced stage to show relative position and size of primary cffica and the first appearance of 

 COBca upon that portion bordering peduncul.ar opening. 



In my Memoir on the Early Stages of Terebratulina, published by the Society, I take up the develop- 

 mental history of Terebratulina from the stage rej^resented in Fig. 105. 



