xra PHYLUM CHORDATA 113 



Division II. Visceral sensory, comprising (a) the fibres which 

 end in visceral mucosae and have to do with visceral sensations ; 

 (6) the fibres ending in taste-buds ; (c) those which terminate in 

 the olfactory epithelium. 



Division III. Somatic motor, consisting of components which 

 terminate in somatic musculature. 



Division IV. Visceral motor, comprising all fibres which terminate 

 in visceral musculature and have to do with visceral movements. 



Urinogenital Organs. In all Craniata there is so close a 

 connection between the organs of renal excretion and those of 

 reproduction that the two systems are conveniently considered 

 together as the urinogenital organs. 



Speaking generally, the excretory organ consists of three parts, 

 all paired and situated along the dorsal wall of the ccelome ; the 

 fore-kidney or pronephros (Fig. 801, A, p. nph.), the mid-kidney or 

 mesonephros (ms. nph.), and the hind-kidney or metanephros (mt. nph.}. 

 Each of these is provided with a duct, the pro- (pn. d.), meso- 

 (msn. d.), or meta-nephric (mt. n. d.) duct, which opens into the 

 cloaca. The gonads (gon.) lie in the crelome suspended to its dorsal 

 wall by a fold of peritoneum : in some cases their products are 

 discharged into the coelome and make their exit by genital pores, 

 but more usually the pronephric duct in the female assumes the 

 functions of an oviduct and the mesonephric duct in the male those 

 of a spermiduct (cf. p. 116). The pronephros is almost always 

 functionless in the adult, and usually disappears altogether. The 

 mesonephros is generally the functional kidney in the lower Crauiata, 

 in which, as a rule, no metanephros is developed, and the meso- 

 nephric duct, in addition to carrying the seminal fluid of the male, 

 acts as a ureter. In the higher forms the mesonephros atrophies, 

 and the metanephros is the functional kidney, the metanephric 

 duct becoming the ureter. 



The kidney meso- or meta-nephros of the adult is a massive 

 gland of a deep red colour made up of convoluted urinary tubules 

 (Fig. 800), separated from one another by connective-tissue con- 

 taining an abundant supply of blood-vessels. The tubules are 

 lined by a single layer of glandular epithelial cells (B, C), and each 

 ends blindly in a globular dilatation, the Malpighian capsule (A, gl.), 

 lined with squamous epithelium. In many of the lower Craniata, 

 a branch goes off from the tubule, near the Malpighian capsule, 

 and, passing to the ventral surface of the kidney, ends in a ciliated 

 funnel-like body (Fig. 801, nst.), resembling the nephrostome of a 

 worm, and, like it, opening into the coalome. At their opposite 

 ends the tubules join with one another, and finally discharge into 

 the ureter. 



The renal arteries branch extensively in the kidney, and give off 

 to each Malpighian capsule a minute afferent artery (Fig. 800, A, va.) : 

 this pushes the wall of the capsule before it, and breaks up into a 



VOL. II H 



