394 PBOF. &. B. HOWES ON THE 



ture, when viewed in relation to the intestine on the one hand and 

 the arteries on the other, is found to answer precisely to the 

 appendix vermiformis of the Mammalia. Like that, it forms a 

 glandular appendage to a diverticulum of the mid-dorsal intes- 

 tinal wall ; like that, it receives its arterial supply from the most 

 posterior offshoot of the superior mesenteric artery. There is 

 here raised the most revolutionary point in my investigation ; 

 and the suggestion would appear, at first sight, to be negatived by 

 the mode of origin of the diverticulum in question in the Pla- 

 giostomes, from the middle instead of the anterior extremity of 

 that which, in them, we are accustomed to regard as the rectum 

 or large intestine. It must not be forgotten, however, that the 

 application of the terms " rectum " and " colon " to the intestines 

 of fishes implies only a conception of rude analogy to the parts 

 so named in the Mammalia. 



The appendix digitif ormis consists of either a digitiforra, as its 

 name implies (PI. II. figs. 8-14), or a slightly coiled structure 

 (HMna, fig. 15). which communicates with the gut by means of a 

 more or less well-marked duct (civ'). It has been described in a 

 general way by various observers for different genera and species*; 

 but neither the gland nor its duct have thus far received the atten- 

 tion which they merit. That the gland arises as a diverticulum 

 of the intestinal wall is clear from the researches of Blanchard 

 (2) f. The intestinal spiral valve of the Plagiostomes usually 

 terminates at a point remote from the origin of this appendix 

 digitiformis and its duct (ex. Saia, fig. 1, v.i.). Parker has re- 

 corded (26) for the valve, in this and other Elasmobranchs, an 

 astonishing range of individual variation in its mode of disposition 

 and total area ; he has failed, however, to lay sufficient stress upon 

 the striking nature of the same in relation to its point of termi- 

 nation posteriorly. In the adult Skate, for example, it may either 

 terminate at a point much farther forwards than that represented 

 in fig. 1 {cf. Parker, I. c. pi. 10. figs. 1 & 8), or at that marked * 

 in the same, thus diminishing the distance between its posterior 

 extremity and the orifice of the duct of the appendix digiti- 

 formis. In Notidanus {Se^^tanclms) the valve extends still fur- 

 ther back, and terminates, in a slightly interrupted but exceed- 

 ingly definite manner (fig. 14, v.i.)., immediately in front of the 



* For rcsitme see Dumuril (7), pp. 157, 158. 



"i" My attention was first drawn to this paper by my friend Dr. Hans Gadow. 



