10 DR. J. F. GEMMILL ON [May 12, 



As is well known through the work mainly of Johannes Miiller 

 (' Yergleichende Anatomie cler Myxinoiden '), the pseudobranch 

 and the choroidal gland are so related to one another in osseous 

 fishes that a pseudobranch is never present in species which have 

 no choroidal gland, while in rare instances only is a choroidal gland 

 present where there is no pseudobranch. It is therefore of con- 

 siderable interest to note that the choroidal glands of the inner 

 or adjacent eyes, in the type of monstrosity under consideration, 

 derive their blood-supply directly from the first aortic root. 

 There is a certain amount of variation in the exact mode of origin 

 of the choroidal and carotid arteries. For instance, cases occuri-ed 

 in which these vessels all arose from the first aortic root on one 

 side only, instead of both roots participating equally as in the 

 specimen figured (PI. II. fig. 12). 



As regards the alimentary canal, there are two mouths, but the 

 pharynx and the rest of the canal are single, the only evidence of 

 duplicity being the presence of two air-bladder diverticula. 



The mesonephros, ureters, bladder, and urinary pore are 

 normal, but the pronephric glomerulus is composite, or may be 

 double. An example of the composite condition is figvired in 

 PI. lY. fig. 29. The glomerulus is larger than in the normal 

 case, and contains two vascular tufts between which is a median 

 compartment that obviously corresponds to the fused adjacent 

 halves of a pair of glomeruli, but has no Wolffian ducts in con- 

 nection with it. In the specimen from which figure 30 (PI. TV.) 

 was taken the two glomeruli are separate, but one of them has 

 only a rudimentary "Wolffian duct arising from its inner side, 

 while the other has none at all. Fig. 29 (PI. lY.) should be 

 compared with figs. 31 and 32 on the same Plate, which show a still 

 gTeater degree of duplicity in the pronephros. 



Of composite muscles, the most important are contained in the 

 median mass mentioned on page 9 as underlying the twin noto- 

 chords, and innervated by the small extra motor roots of the 

 composite spinal cord. This muscular mass is segmented serially 

 by septa which correspond exactly with the septa of the outer 

 (normal) lateral muscles. In the head-region some small and 

 intricately arranged muscles are found connected with the 

 cartilages which represent the reduced adjacent Meckelian and 

 palato-quadrate bars. These muscles are obviously rudiments 

 of adjacent mandibular and temporal muscles. It has been noted 

 previously that there are no external rectus muscles in connection 

 with the adjacent eyes, and that the superior obliques are either 

 rudimentary or entirely absent. 



A typical specimen of the second subgroup of Class I. will next 

 be described, i. e. a specimen which shows the tvnn brains uniting 

 at the medulla oblongata. 



The structure of the cranial skeleton in this type agrees with 

 that of the monstrosity last described, except that the place of 

 union of the skeletal elements is carried further back. This gives 



