1883.] 



TESTIMONY TO GENERAL HOMOLOGY. 



3.t1 



first a ray diverging from, or near to, the articular interspace between 

 the scapula and coracoid, or the ilium and pubis. This primitive 

 condition of limb he terms, in Fishes, the " basipterygial bar'", and 

 represents it as such in his figure 346, under the letters mpt, of a 

 section of the embryonal pectoral fin in ScijlUum stellare. 



So, in Fishes, " In both fins the skeleton in its earliest stage 

 consists of a bar springing from the posterior side of the pectoral 

 or pelvic girdle, and running backwards parallel to the long axis of 

 the body. The outer side of this bar is continued into a plate 

 which extends into the fin, and which becomes very early segmented 

 into a series of parallel rays at right angles to the longitudinal bar^ 

 In other words, the primitive skeleton of both the fins consists of a 

 longitudinal bar running along the base of the fin, and giving off at 

 right angles a series of rays which pass into the fin. The longi- 

 tudinal bar, which may be called " basipterygium,'' is moreover 

 continuous in front with the pectoral or pelvic girdle as the case 

 may be"^. 



Gegenbaurand his followers believed the " bar" and " rays" to be 

 contemporaneous in appearance ; and truly they come early into view 

 and follow quickly. Balfour, however, derived, from apparently 

 closer or earlier observation, the conviction that they showed two 

 stages, and that the " rays " were consecutive in appearance to the 

 "bar"^ 



If this view, as is probable, be preferably accepted, the "diverging 

 appendages " of the haemal arches or so-called " girdles," intervening 

 between the scapular and pelvic ones, may be viewed as " embryonal 

 limbs " arrested at the " bar-stage." It may be objected that such 

 "costal appendages," as a rule, are lamellar, or in form of a "plate" 

 rather than a " bar ;" but such is the shape assumed by the pri- 



Chondropterj-gian embryonal fin (after Balfour). 



mordial fin, when the " basipterygium " (annexed figure, bp) be- 

 comes the " metapterygium " (ib. mp), or sustainer of the " meso- 

 pterygium," or rudiment of the consecutive or future "pro- and 

 mesopterygia " («, 6). 



^ Tom. cit. p. 502. 

 4 Tom. cit. p. 501. 



24* . 



1 Tow. cjY. p. 504. 

 •■' Tom. cit. p. 502. 



