786 MR FRANK J. COLE 
anterior ventral fin rays. According to BasHrorD Deay, the fin rays arise as unbranched 
structures in Bdellostoma. 
In front of the ventral bar there were in the specimen figured twenty-one free fin. 
rays, all situated behind the cloaca, which extend a short distance within the contour 
of the body between the slime sacks, and none of which were bifurcated. AvyErs and 
JACKSON figure fourteen, with all but one bifurcated. 
I may mention here that in Bdellostoma AyeERs and Jackson describe “a very thin 
irregular sheet of cartilage in the wall of the cloaca, especially in the anal region,” which 
they believe possibly “serves to expand the anal opening in anal respiration” (p. 217). 
I have failed to find this cartilage in Myzxine either by dissection or in serial sections. 
The minute structure of the cartilage of the fin rays and dorsal and ventral bars 
indicates that it is an extreme variety of soft cartilage, but not so primitive as that of 
the branchial skeleton. Its staining reactions resemble those of the latter cartilage, but 
there is a tendency in the direction of differentiation. It consists of large cells, each 
surrounded by a distinct deeply staining zone that I take to represent the cell capsule, 
embedded in a practically continuous reticulum of what is clearly cement. The inter- 
cellular substance or cement is, however, distinctly weaker than in typical soft car- 
tilage, but it is, on the other hand, more continuous or reticular than in the hard 
cartilage, thus accentuating the difference between typical hard and soft cartilage 
already referred to. 
April 26, 1905. 
N. EXPLANATION OF THE PLATES. 
REFERENCE LETTERS. 
a. d. p. Anterior arch of the dental plate. ch. c. Chordal cells forming the notochordal 
a. d. p.’ Posterior ort Ba “Jelly.” 
a. d. p.” Posterior internal es aes ch. ep. Chordal epithelium, 
a. t. b. Anterior transverse bar of the nasal capsule. cl. Cloaca. 
a. t. v. b, Anterior transverse velar bar. cr. Membranous cranium. 
au. c, Auditory capsule. cs. Centosomes of the cartilage cell. 
au. f. Auditory foramen. c. sb. Cement substance of the hard cartilage. 
b. p.* Anterior, middle, and posterior segments ct, c. Cartilage cell. 
of the basal plate. d. ces. ct. Ductus cesophago-cutaneus. 
br. a. First ‘‘ branchial” arch. d, t. Median dorsal tooth. 
br. a.” Second “branchial” arch. In fig. 1, con- | e. 0. p.’ External bar of the anterior segment of 
sisting of separated upper and lower the basal plate. 
divisions. e. l. b, External lateral velar bar. 
br. ap.’ Left | branchial epee e. . b.’ Short rod of soft cartilage connecting 
br. ap.” Right above with the posterior extremity of 
c. ¢. Cornual cartilage, the inferior process of the “ pterygo- 
c. ct. c. Capsule of the cartilage cell. quadrate” (cp. figs. 1 and 2), 
c. g. p. Tendon of the M. copulo-glossus profundus el. ext. Elastica externa of the notochordal sheath, 
(P. Ftrerineer) cut across (=the f.* The four fenestre of the skull, 
tendon of the protractor muscle of the | “jin” Dorsal, caudal, and the adipose pre-anal 
dental plate, Ayers and Jackson). “fins,” 
