SKATE. 275 



structures which are peculiar to Elasmobranchii have been figured. 



They run towards the head, where their inner ends are situated in 



close contact. Their length varies, the most anterior being short, 



the posterior long. Their apertures are easily found. The tubes are 



dilated at their inner extremities and possess in this species numerous 



lateral saccules. The nerves pass along the septa between these sac- 



cules, radiating from the centre. They form a plexus in the walls of 



the saccules, the ultimate fibrils of which are probably continuous 



with hair cells in the lining epithelium. The jelly filling these tubes 



is firm, and is secreted by goblet cells scattered on the walls. 



The lateral line is not indicated in this figure. See Merkel, Endigun- 



gen der Sensibeln Nerven, &c.; Rostock, 1880, p. 33, PI. II. Fig. 10 ; and 



Leydig, Beitrage zur Mikr. Anat. &c., der Rochen und Haien, Leipzig, 1852, 



p. 37. The ampullae are also described by the same authors, see Merkel, 



p. 43 ; Leydig, p. 41. 



h. Middle lobe of the liver, which is trilobed in this species, cut short. The 

 right and left lobes are seen on either side of the aperture made in 

 the abdominal walls. 



i. Gall-bladder, in the fissure between the right and central lobes. 

 The letters h and i are placed over the coracoidal bar. 



k. Stomach, which has the form of a siphon. Blood-vessels are seen 

 arising from the concave edge of the organ and uniting to form a 

 vessel which passes towards the liver and is one of the factors of the 

 portal system. 



/. The spleen. 



m. The intestine with its anterior wall removed to show the spiral valve 

 formed by its mucous membrane. Such a valve is found in all Elas- 

 mobranchii, in Ganoidei (rudimentary in Lepidosteus) and Dipnoi. The 

 inclination, &c., of the folds varies much in the different genera. 



n. Rectum. The line points to the spot where the rectal gland, found in 

 all Elasmobranchii, opens into it on its dorsal aspect. 



o. Dilated duodenum or Bursa Entiana. It receives the bile and pancreatic 

 ducts. The pyloric aperture is placed on a nipple-like projection. 



/. The line points to the fold which lies dorsal to the anal aperture into 

 the cloaca, and separates it from a recess into which open the two 

 oviducts laterally and the urethral canal medianly. In the male there 

 is a urogenital papilla on the dorsal wall of the cloaca. 



q. Right porus abdominalis or external aperture of one of the two canals 

 by which the abdominal cavity communicates with the exterior in 

 Elasmobranchii, Dipnoi, some Ganoidei, and a few Teleostei. 



r. The two-lobed ventral fins. In a male the claspers would be situated 

 between the inner lobes of these fins and the root of the tail. 



s. Tail cut short 



T 2 



