INTRODUCTION. X1U. 



I should propose to divide Ascidire Compositse into two 

 sections to which Sluiter's names "Merosomata" and 

 " Holosomata " might well be applied. If Dr. Sluiter will 

 accept this modification in the sense of his terms I shall be 

 glad to adopt them. It will leave his term Merosomata 

 unaltered, except for the exclusion of the family Pyrosomidae; 

 but will mean that Holosomata is used in a very restricted 

 sense as indicating only the remaining Compound Ascidians, 

 i.e., the two families Botryllidre and Poly sty elidse. If, how- 

 ever, Dr. Sluiter objects to my proposed change in the 

 restriction of his names, the only course open to me will be to 

 propose two new terms for the sections of Ascidise Compositse 

 which I desire to recognise. I should suggest in this case 

 " Pectosomata " for the compact-bodied families Botrylliclse 

 and Polystyelidse, and " Chalarosomata " for the remaining 

 families with extended or divided bodies. 



I divide, then, the Tunicata into three main sections or 

 orders : 



I. LARVACEA, the free-swimming, permanently-tailed, 



larva-like, mostly minute Appendicularians. 

 II. THALIACEA, the free-swimming, highly modified, 



tail-less, somewhat barrel-shaped, Salps and 



Doliolums and their allies. 

 III. ASCIDIACEA, the sessile, mostly fixed, Simple and 



Compound Ascidians. 



The collection I am describing does not contain representa- 

 tives of the two first orders, nor yet of the exceptionally 

 free swimming Pt/rosoma from the third section ; so we have 

 only to do with the ordinary Simple and Compound Ascidians, 

 which are all built up on one general morphological plan, each 

 member of the colony of a Compound Ascidian being com- 

 parable in structure with a single solitary Simple Ascidian. It 

 will serve, then, as an introduction to the descriptions of the 

 various forms in this catalogue if I give here a short account 



