XV111. INTRODUCTION. 



the three shapes of Ascidiozooid characteristic of (fig. 6) a 

 Botryllid, (fig. 7) a Distomid, and (fig. 8) a Polyclinid; 

 while figures 1 to 4 represent whole colonies of (fig. 1) a 

 Distomid, (fig. 2) a Didemnid, (fig. 3) a Polyclinid, and 

 (fig. 4) a Botryllid. These figures may help in reading the 

 descriptions of Compound Ascidians in the latter part of 

 this Catalogue. 



In consideration of the great importance of the matter, 

 and the use made of it in definitions of the group Tunicata 

 and its larger divisions (see pp. 1, 2, &c.), I have given, on 

 Plate C, a series of diagrammatic figures illustrating the 

 more note-worthy stages in the embryology and early life- 

 history of a typical Tunicate. Figure 1 shows the ovum 

 and spermatozoon, figs. 2 to 6 successive embryonic stages, 

 figs. 7 to 9 the free-swimming tailed "Chordate" larva, and 

 figs. 10 to 12 the process of degeneration into the sedentary 

 adult Ascidian, such as those described from. Australia in 

 the following pages. 



