CHAO: DIGESTIVE SYSTEM OF CUNNER 



to the labrids described by Al-Hussaini (1947b). 

 The buccal valve (Figure 2) is similar to that 

 of Julis aijgiila reported by Gohar and Latif 

 (1961), except for the obvious thickening of 

 the mucous layer of the anterior surface in 

 juvenile cunners. The rather short relative 

 length of the gut of the cunner, i.e., the post- 

 pharyngeal portion of the alimentary tract, 

 is about 0.8-1.0 of standard length. The exten- 

 sive vascularization of the serosa and adventitia 

 of the rectum and the strong alkaline phospha- 

 tase activity of the rectal mucosa indicate that 

 this region is very active in absorption and/or 

 secretion. The S-loop of the intestine may be 

 unique because it was not described for other 

 labrids by Suyehiro (1942) and Gohar and Latif 

 (1959, 1961) nor in some other stomachless fishes 

 reported by Babkin and Bowie (1928) and 

 Al-Hussaini (1949a). Bullock (1967) recorded 

 a similar flexure in the posterior portion of 

 the intestine of Gambnsia affiuis. The S-loop 

 was somewhat straightened by large amounts 

 of food in the lumen. Alkaline phosphatase 

 tests show weak positive reaction in the S-loop. 

 The significance of the loop may be mechanical 

 rather than physiological. There are no suc- 

 cessive constrictions of the intestine in cunner 

 as observed by Gohar and Latif (1961) in 

 P^eudoscarus harid and credited by those 

 authors to J»//.s- aygula. 



Epidermal mucous secreting cells in the 

 epithelium of the alimentary tract of cunner 

 are mostly concentrated in the postpharyngeal 

 cavity and the esophagus and on the anal 

 papillae. These cells have no stalklike elonga- 

 tion at the bottom of the globule nor a narrow 

 necklike structure before the open end (Figures 

 3, 4, 6, 9, 20) as do those of the intestine and 

 rectum (Figures 12, 14, 15). No precise histo- 

 chemical differentiation of these mucous cells 

 was obtained. These different types of mucous 

 cells have been reported by Al-Hussaini (1947a). 

 Gohar and Latif (1961),' Mohsin (1962). Bul- 

 lock (1967), Western (1969), and Bucke (1971) 

 in various fishes. Al-Hussaini (1949b) and 

 Bullock (1963). following the terminology of 

 Baker (1942), described the free border of 

 the absorptive columnar cells in the intestine 

 as divided into a superficial layer, a canal 

 layer (or microvilli region), and a granular 



layer. These were also distinct in the cunner 

 gut. 



The rodlet cells are similar to those dis- 

 cussed by Bullock (1963) in the intestine of 

 salmonid fishes and the pear-shaped cell of 

 Al-Hussaini (1949b) recorded in Gobio gobio. 

 These cells appeared throughout the gut except 

 in the anterior intestinal bulb and the posterior 

 rectum as in Gdnibiisia affiuis (Bullock, 1967). 

 They are also found in the bile duct, gall- 

 bladder, and collecting duct of the kidney of 

 the cunner. Bullock (1963) also described the 

 appearance of rodlet cells in the kidney of 

 CatostoniK.s species. Al-Hussaini (1964) de- 

 scribed the mitosis of the pear-shaped cell in 

 Cyprinus carpio. He stated that experimental 

 evidence indicated the pear-shaped cell may 

 originate from goblet cells in C. carpio and 

 Gobio gobio and from wandering blood or 

 connective tissue cells in RutilHs nitilns. No 

 comparable evidence of the division nor origin 

 of the rodlet cells was found in this study. 

 Bishop and Odense (1966) proposed that the 

 pear-shaped cell may be a possible enzyme 

 source in the intestine of the cod, Gadus morhua. 

 But the negative phosphatase reactions of the 

 rodlet cells in the cunner agree with Bullock's 

 1963 findings for salmonids. Different cyto- 

 logical or developmental stages of rodlet cells 

 were observed in the mucosa of the bile duct, 

 gallbladder, and intestine. The rodlet cells and 

 their empty capsules, which have no distinct 

 nuclei, were partially or entirely free from the 

 mucosa of the bile duct. Occasionally, ejection 

 of granules from the rodlet cells was seen. 

 Rodlet cells have not been described in labrids 

 prior to the present account. The question 

 remains as to whether they are normal cells 

 or coccidian parasites (Plehn, 1906). 



The submucosal layer of the cunner gut 

 is composed of a rather homogeneous fibrous 

 connective tissue. There is neither muscularis 

 mucosa nor lamina propria. The stratum com- 

 pactum in various fishes has been discussed 

 by Al-Hussaini (1947a), Burnstock (1959). 

 Gohar and Latif (1961), Mohsin (1962), Bul- 

 lock (1963). and Bucke (1971). In cunner it 

 is a thin layer of regularly arranged fibers 

 immediately beneath the mucosa. In oblique 

 sections, fibrils can be seen passing from the 



581 



