AÏRIAL TENTAGLES IN TUNIGATA. 57 



In tlie simple Ascidiaii Bathyoncus mirabilis, from the Southern 

 Océan, at a deplh of 1600 fatlioms, tliere are two circlets of minute 

 tentacular processes wliicli project from the inner surface of the 

 cloacal wall close to the alrial aperture. Thèse atrial tentacles are 

 ail of the same size, aud are placed at about their own length 

 apart from one another (see Report on Tunicata of Challenger 

 Exp., Part. I, Vol. VI, 1882, p. 167, and PI. xxiv, fig. 12, at. t.). 



The Ascidiozooids of the compound (?) Ascidian Goodsirna pla- 

 centa, from the Cape of good Hope, hâve also atrial tentacles, verv 

 much tihe tliose of Bathyoncus mirabilis , but forming a single 

 séries. In the original description {op. cit., Part. II, Vol. XIV, 1886, 

 p. 331, and PI. xliii, fig. 10), I wrote as follows : — « At the base 

 of the atrial siphon, where the invaginated layer of test ends, 

 there is a slight ridge which bears a séries of small tentacles i)ro- 

 jecting treely into the peribranchial cavity. Thèse atrial tentacles 

 are much smaller than the ordinary or JDranchial tentacles, and 

 there are only twelve of them. The position of the atrial ten- 

 tacles in relation to the atrial siphon corresponds exactly to the 

 position of the branchial tentacles at the base of the branchial siphon, 

 but their use, at the entrance to the peribranchial cavity, is not 

 obvions. It has been observed in some simple Ascidians that the 

 current of water wliich usually flows in at the branchial aperture 

 and out at the atrial is occasionally reversed for a short period, the 

 atrial aperture becoming inhalent. Possibly in the présent species 

 tins habit may hâve become so marked as to hâve favoured ihe 

 development of a circle of atrial tentacles which would act as 

 tactile organs waving in the current of water entering the animal ». 



During- the rast few years I hâve found similar atrial tentacles in 

 at least three new species of the compound (?) Ascidian genus Cliori- 

 zoco)'7nus, viz., Ch. Sydney ensis, Ch. leucophœus, and Ch. suh- 

 fuscus, ail from Australia. In oach case they form a single circlet, 

 as in Goodsiria placenta, and there are about 20 tentacles. They 

 are briefly referred to in my « Revised Classification of the Tuni- 

 cata » (1891), at p. 636, and will be figured in the forthcoming 

 « Catalogue of Tunicata of Australian Muséum ». And lastly Julin 

 has made the interesting discovery that atrial tentacles are also 

 présent in Styelopsis grossularia. 



I hâve queried (?) above the gênera Goodsiria and Chorizo- 



