TUNICATA. 



483 



Salpa maxima. 



extremities. The efferent orifice {Jig. 184, 6) is simple and tu- 

 bular : it can be closed by a 

 sphincter when the outer tu- 

 nic expands, the water then 

 flowing in by the opposite 

 orifice : this is in the form of 

 a transverse slit, having an 

 upper lip (a) and a lower one 

 {(f) : the latter forms a semi- 

 lunar valve, allow^ing the entry 

 and preventing the exit of water. The muscular fibres of the mantle, 

 or membrane lining the cartilaginous tunic, are arranged in flattened, 

 often subannular bands; their elementary fibre is plicated. The 

 mouth and stomach, the liver and the heart, are aggregated in a small 

 mass or * nucleus '(c), near the anterior aperture of the tunic ; the intes- 

 tine extends towards the opposite aperture, and terminates freely in the 

 common cavity of the mantle. The intestine in Salpa gibbosa has 

 two caeca which project into the centre of the loop. In Salpa zonaria, 

 the liver envelopes nearly all the intestinal canal, and consists of 

 a mass of caecal tubes, with a few small appendages near their 

 free ends.* The group of small yellowish ganglia is situated just 

 above the posterior attachment of the branchia : near it is often 

 observed a pigment-speck or ocellus {/). A single narrow plicated 

 ribband-shaped branchia (d) extends obliquely lengthwise across the 

 pallial cavity. The heart (e) is elongated, and in some species slightly 

 curved and sacculated ; it communicates with a large vessel at each 

 extremity, one of which is ramified principally upon the visceral 

 mass ; the other upon the branchia and the muscular tunics. The 

 blood passes into extensive venous sinuses before returning to the 

 heart : its course is oscillatory, as in the Ascidians. 



The sexes are distinct in the Salpians, as in the solitary Ascidians. 

 Tlie testis is described by Krohn as of an oblong form, single, lodged 

 in the centre of the nucleus in Salpa maxima, in which it consists of 

 numerous delicate seminiferous tubes, filled with a white fluid, and 

 opening by a short canal into the common cavity of the body. The 

 two oblong bodies, sometimes of a violet colour, attached to the mantle 

 at the dorsal aspect of the test, have been regarded as ovaria. Sars, 

 however, affirms that the solitary individuals of the Salpae are sex- 

 less. The germinative tube, in which the chain of young salpae {Jig. 

 185.) is contained, winds round the visceral nucleus, hanging freely 

 by one end in the cavity of the mantle, and being attached by the 

 other end to the back of the nucleus. 



• CCXCIX. 

 II 2 



