106 m CHARD EVANS. 



spicules shown in Pig. 3. a represents m of Fig. 3 ; /5 is an enlarged drawing 

 of g of Fig. 3 ; and c shows the end of the amphidisc when looked down 

 upon. Note the serrated edge. 



Fig. 5 (x 665). — A young amphioxea shown inside the scleroblast. It 

 should be specially compared with the Fig. 6, a, which represents the 

 early stage of the amphidisc. Both are drawn on the same scale, and on 

 comparison it will be clearly seen that the spicule represented in Fig. 6, a, 

 cannot be a young amphioxea. 



Fig. 6 ( x 665). — A representation of an early stage, a ; intermediate stage, 

 b; and a fully-grown stage, c, of the amphidisc. Each spicule is situated 

 inside the scleroblast which produced it. The cells themselves are amoeboid 

 in character. 



Fig. 7 (X 225). — This figure represents a side view of the somewhat pro- 

 blematic body discussed in the footnote on p. 74, and described as having a 

 basket-like form. It is covered with spicules {sp.) of the amphioxea type be- 

 longing to group b (compare Fig. 3,/). 



PLATE 2. 



Fig, 8 (x 565).— A representation of the cells which later on in the 

 development become the yolk-cells of the gemniule. On tiie left side of the 

 figure the cells are seen coming together in virtue of their power of wander- 

 ing. On the right side a portion of a much bigger group of cells is seen. 

 Tiie group in question is situated in the interior of one of the columns of 

 tissue which support the dermal membrane. Note that the jirotoplasni of the 

 cells is absolutely clear, and that the nucleus is not vesicular. 



Fig. 9 (X 1)50). — A representation, more highly magnified, of a slightly 

 later stage than that shown in Fig. 8. Note that the protoplasm is becoming 

 slightly granular. 



Fig. 10 (x 950). — A representation of a slightly later stage than that 

 shown in Fig. 9. Note that the protoplasm has become still more 

 granular. 



Fig. 11 (x 130). — A representation of the gemmule at a stage slij;htly 

 later than that shown in Fig. 10. Note that the granules in the cells have 

 increased to a considerable extent in size, but that their internal structure is 

 not so dense as at later stages. Also note that a great number of cells 

 possessing different characters are aggregated round the central cells {yo. 

 cells). These cells seem to have been derived from the sponge at a later stage 

 than the yolk-cells, and constitute a different class both as regards their 

 origin and fate. 



Fig. 1\(( (X 950). — A representation, more highly magnified, of a portion 

 of the section shown in Fig. 11. Note the yolk-cells {yo. cells) with then- 



