REPORT ON THE TUNICATA. 57 



ganglion. These, with the possible addition of the languct and the ciliated groove in 

 the dorsal tubercle, or opening of the subneural gland, are the only sense organs known. 



There is no circle of tentacles in the branchial siphon. The peripharyngeal bands 

 are in their usual position in the Tunicata, running round the front of the branchial 

 sac from the anterior extremity of the endostyle to the front of the dorsal lamina. 

 There is a subneural gland underlying the ganglion. Its duct leads forwards, and opens 

 into the front of the branchial sac just anterior to the peripharyngeal bands. The 

 opening widens out to form a richly ciliated groove, which may be either straight and 

 elongated antero-posteriorly (PI. VI. fig. 11) or curved upon itself to form a more or 

 less elaborate " dorsal tubercle." 



The endostyle is long and straight. It runs to the posterior end of the Itranchial 

 sac, where it and the dorsal lamina meet on the opposite sides of the cesophagcal 

 aperture. The heart is placed near the posterior end of the endostyle, ventrally to the 

 oesophagus. 



The alimentary canal is relatively small, and is coiled up along with the testis to 

 form a small compact opaque mass, the "nucleus" or visceral mass (PI. IX. fig. 7, vise). 

 This arrangement of the viscera is characteristic of Saljm, and distinguishes it from the 

 next genus Cyclosalpa, in which the alimentary canal is stretched out, and consequently 

 no " nucleus " is formed. The anus opens into the peribranchial cavity on the dorsal 

 surface of the nucleus (Fig. 7, a). 



The figure (Fig. 7, p. 55) represents an aggregated or sexual Salpa which in an 

 earlier period of its existence was a member of a chain, and consequently it shows 

 a testis and a developing embryo. The ova (always few in number, usually only one) 

 appear at a very early period in the developing chain Salpa, while it is still a part of 

 the gemmiparous stolon in the body of the solitary Salpa; while the testis, on the other 

 hand, does not develop until much later. This protogyny prevents self-fertilisation. 

 The ovum is situated in the median dorsal line, not far from the posterior end of the 

 body, and lies at first in a blood-sinus of the mantle, enclosed in an ovisac, the wall of 

 which is prolonged to form a narrow tube, the oviduct, which opens into the peri- 

 branchial cavity on its right side. Spermatozoa from another and older sexual Salpa, 

 belonging to a different chain, gain access by means of this oviduct and fertilise the 

 ovum. 



The embryonic development is carried on in a " brood-pouch" formed by an enlarge- 

 ment and modification of the oviduct into a sac which projects into the peribranchial 

 cavity, and eventually ruptures so as to set the embryo free. At an early period in its 

 development, part of the wall of the ovisac, probably along with part of the embryo 

 itself, becomes converted into the " placenta," an organ in which the foetal and maternal 

 blood-streams circulate in close proximity, or actually coalesce during one period. At 

 a somewhat later stage, a number of cells placed near the posterior end of the body 



(ZOOL. CHALL. EXP.— PART LXXVI.— 1888.) Gggg 8 



