THE "TRITON TUNICATA. 101 



papilla placed at each point of intersection with the median or chief trans- 

 verse membrane (tr' in the figs.) and the internal longitudinal bars. These 

 papillae are usually rather smaller than those at the angles of the meshes, 

 but in some cases (as is shown in the upper part of fig. 2) the papillae may be 

 all of the same size. I have found the chief papillae varying in size from a little 

 less than one-half* the breadth of the mesh to (in the case of the "Triton" 

 specimen) the entire breadth. In fig. 1 the papillae have been omitted, in 

 order that the transverse membranes might be clearly seen. 



Returning to the " Triton " specimen, the margin of the anus was expanded 

 and more deeply indented than is shown in Heller's figure. t The oviduct was 

 found full of ova, some of which were also discovered in the peribranchial 

 cavity ; and the pigmented glands at the aperture of the vas deferens seemed to 

 form a larger and more conspicuous mass than usual. 



Order II.— THALIACEA. 



Both families of this order, the Doliolidae and the Salpidae, are represented 

 in the collection. 



Family I. — Doliolidae. 



Doliolum denticulatum, Quoyand Gaimard (Pis. XVIII., XIX., and XX.). 



The five or six thousand specimens of Doliolum in the collection are, I was 

 astonished to find, all one form, and this I have identified with the sexual 

 generation of Doliolum denticulatum.^ This species was first described and 

 figured by Quoy and Gaimard, the founders of the genus, in the zoology of 

 the voyage of the " Astrolabe,"§ in 1835. It had been found in the Malay 

 Archipelago near the islands of Amboyna and Vanikoro. Sixteen years later 

 Huxley |] published his observations made upon certain Tunicata during the 

 voyage of the "Rattlesnake." In this paper very considerable additions are 

 made to the knowledge of the structure of Doliolum, and the relations in 



* In Heller's figure they are about one-fourth, of the breadth of the rnesh. 



t hoc. tit., Taf. v. fig. 8. 



% As will be pointed out in the following description, there are a "number of details, especially in 

 the branchial sac, in which these " Triton " specimens differ from the accounts of Doliolum denticula- 

 tum given, by Keferstein and Ehlers (Zoologische Beitrcige, 1861) and by Grobben (Arbeiten aus 

 dem. Zoolog. Instlt. der Univ. Wien, 1882). As, however, they agree with those authors' descriptions 

 in the more important anatomical features, and as they could not be referred to any other known 

 species, I prefer to consider them as a variety of Doliolum denticulatum. It is improbable that they are 

 an undescribed species, since they are apparently so common in the North Atlantic. Doliolum den- 

 ticulatum is probably rather a variable form. 



§ "Voyage de cUcouvertes de 1' Astrolabe," Zoologie, T. iii. pt. 2, p. 599; Atlas, Mollusques, 

 pi. lxxxix. figs. 25-28. Paris, 1835. 



|| "Eemarks upon Appendicularia and Doliolium," &c, Phil. Trans, for 1851, part 2, p. 599, pi. 

 xviii. 



VOL. XXXII. PART I. S 



