446 PEOr. W. A. HEEDMAN OK BEITISH TUKICATA. 



marked as to have favoured the development of a circle of atrial 

 tentacles, which would act as tactile organs waving in the current 

 ■of water entering the animal." 



During the last few years I have found similar atrial tentacles 

 in at least three new species of the compound (?) ascidian genus 

 Cliorizocormus, viz., Cli. sydneyensis, Cli. leucoplimts, and Cli. suh- 

 fiiscus, all from Australia. In each case they form a single 

 circlet, as in Goodsiria placerda, and there are about twenty 

 tentacles. They are briefly referred to in my " Eevised Classi- 

 fication of the Tunicata " (1891), at page 636, and will be figured 

 in the forthcoming ' Catalogue of Tunicata in the Australian 

 Museum.' Julin has made the interesting discovery that atrial 

 tentacles are also present in Styclopsis yrossularia. I have 

 likewise found them in that form, and now I can add Polycarpa 

 glomerata to the list of species in which it is known that the 

 organs are present. 



I have queried above the genera Goodsiria and Cliorizocormus 

 as being compound ascidians because they belong to the family 

 Poly sty elidse, in regard to which it must be considered still 

 doubtful whether the masses of ascidiozooids are true colonies. 

 But although they may be colonial forms now, there can be no 

 doubt that phylogenetically the Polystyelidse are closely related to 

 the subfamily Styelinae of the Cynthiidse, the subfamily to which 

 Bathyoncus, Folycarpa, and Styelopsis all belong. So we arrive at 

 the interesting conclusion that the five genera in which up to now 

 atrial tentacles have been noticed, although differing widely from 

 one another in appearance, structure, and tabitat, are yet phylo- 

 genetically rather closely related. I think it not unlikely that 

 atrial tentacles will be found, if looked for, in other members of 

 the groups Styelinse and Polystyelidse. 



Another point : it is an interesting fact, and may have some 

 significance, that — putting aside Bathyoncus mirahilis, in regard 

 to the conditions of life of which we know nothing — all the six 

 other species in which atrial tentacles have as yet been demon- 

 strated form either colonies or aggregations, ^.e. they have numbers 

 of small individuals or ascidiozooids massed together. It is quite 

 conceivable that, under these crowded conditions, it may be 

 some advantage to the animals to have the power (to return to 

 the suggestion I made in the ' Challenger' Keport) of frequently 

 reversing the current of water or of using the atrial for a time 

 as the inhalent aperture — possibly, for example, because of being 

 so placed amongst neighbours that the atrial siphon is able to 



