Introduction. 



Originally it was my intention to study the Northern and Arctic Botryllids from 

 a systematic, geographical point of view. I soon found, however, that such an 

 investigation could only be accomplished in conjunction vvith a renewed survey of 

 the speeies to which they belong and also of the basis on which the classification 

 of the family rests. 



Until quite recently only little attention has been paid to the anatomical struc- 

 ture of the individuals of the family. The descriptions hitherto given of the speeies 

 have been almost exclusively based on external characters. Giard ' who, according 

 to Lahille 2 , reported thirty-eight speeies of the genera Bolryllus or Botrylloides from 

 a single locality, Roscoff, made use of external features only by vvay of specific 

 distinctions, relying especially on the varying colouration of the colonies: «Bien qu'on 

 puisse dire pour les Botrylles comme pour les fleurs, Nimium ne crede colori, la 

 couleur est peut-étre encore ce qui nous fournit les plus surs moyens de classification» 

 (l. c. p. 620). To that character— the colouration of the colonies — thus made use 

 of by Giard and by many other zoologists too, for distinguishing speeies, there may 

 be added another external feature, viz. the thickness of the colonies, and it is this 

 character upon which both Lamarck's and Drasche's subdivision of the genera 

 respectively rest. This classification of the Botryllidce was adopted by Della Valle 

 and even by Herdman with hardly a word of discussion and, faute de mieux, may 

 be said to hold the field. On its basis, however, the determination of the Botryllid 

 speeies is a matter of great difficulty, not to say of impossibility, for, however won- 

 derful the brilliancy of colour and the variability of shape in the specimens may be, 

 all modern zoologists are agreed that those characters entirely lack reliability from a 

 scientific point of view. 



It is only certain organ systems of the Botryllids, such as the branchial sac and 

 the alimentary canal that have been as yet thoroughly investigated, the reproduetive 

 organs for instance having been only very incompletely studied. Della Valle 3 did 

 indeed describe the reproduetive organs, but though the results of his investigation, even 

 if not quite exact, should, one would have thought, have prompted others to follow in his 

 footsteps, very little attention has been paid to them by writers since his day. Pizon 4 , 



1 Giard, A., Recherches sur les Ascidies composées ou Synascidies. Arcli. Zool. expér. Vol. 1. Paris 1872. 



2 Lahille, F., Recherches sur les Tuniciers. Toulouse 1890. 



3 Della Valle, A., Nuove coutribuzioni alla Storia naturale delle Ascidie composte del Golfo di Napoli. 

 Atti Acc. Lincei Mem. Ser. 3. Vol. 10. Roma 1881. 



4 Pizon, M. A., Histoire de la Blastogénese chez les Botryllidés. Ann. Sci. nat. Sér. 7. Vol. 14. Paris 1893. 



