The Embryology of Chlamydoselachus 613 



older embryos drawn at an earlier date and recorded in Dean's notebook. Here the 

 ''List" reads for the next stage — "Embr. of mm. 123 entire. Ventral (head) dorsal head". 

 I do not find such figures, but I do find a full-length lateral drawing and another of a dorsal 

 head, both marked "124". These drawings I take to have been made from the specimen 

 referred to — the difference of one mm. being insignificant. Whether or not the "ventral 

 head" was drawn cannot be said. But on the plates as made up by Dean, I find occasional 

 scars on the board where drawings have been removed. It is of course possible that the 

 drawing of the "ventral head" of this stage has been removed and lost. The drawings of 

 the 124'mm. embryo will now be studied in comparison with those of the 103'mm. 

 specimen — the preceeding stage. 



Head in Dorsal Aspect. — When comparison is made of the drawing (Figure 44, 

 plate IV) of the "dorsal head" of the 124'mm. embryo, with that of the head of the 103- 

 mm. fish (Figure 41, plate IV), it looks older, more finished. The head of the 124'mm. 

 fish looks longer and narrower, and the eyes are less conspicuous. The spiracle is not 

 visible, being probably too small to show in this low magnification (x 2 + , the same 

 magnification as Figure 45, plate IV, the fish in lateral view). The gilhcovers are some- 

 what distended but reveal no trace of gilbfilaments. The lateraMine system shows on the 

 trunk but is indistinct on the head. The pectorals are smaller. One wishes for the draw 

 ing of the "ventral head" to show the form of the mouth and the ventral parts of the gill' 

 covers, especially the first. 



Full-length Lateral View. — It was noted that the 103'mm. fish, portrayed in lateral 

 view in Figure 42, plate IV, showed some decided resemblance to the adult form. How 

 much more is this true of the 124'mm. specimen seen in Figure 45, plate IV. Here the 

 whole fish is plainly a young Chlamydoselachus. Note the pointed snout, the forwardly 

 placed nasal aperture, the eye in about the vertical of the middle of the mouth, the long 

 lower jaw reaching close to the end of the snout. The gill-covers (the first much the 

 larger) decrease in length normally from 1st to 6th, and have their dorsal edges backwardly 

 bent as in the adult. No gill-filaments can be seen. The spiracle is not shown in this 

 drawing, even though the original measures 257 mm. in length — i.e., x 2 + • The pectoral 

 fin is much larger than that of the 103-mm. specimen, but the pelvic is of about the same 

 siz;e. The dorsal and anal are somewhat smaller than these fins are in the younger fish. 

 The back is nearly straight from head to dorsal fin. The body has elongated, not in the 

 tail region but in the body proper, i.e., between pectoral and pelvic fins. The tail ends in 

 a fine-pointed caudal fin which droops slightly downward. The soft parts of the caudal 

 fin are smaller than those of the 103-mm. fish. The lateral line is well developed and 

 shows an interesting curvature behind the vertical through the tips of caudal and anal. 



An Embryo of 175 mm. and its Yolk Sac 



The "List" next calls for "Embr. of mm. 175, entire, dorsal aspect with yolk". This 

 I find as portrayed in Figure 11, plate I. In the original drawing, the fish, measured 

 carefully over the curves, is 205-mm. long and the yolk sac measures 92 x 90 mm. On the 

 page of Dean's notebook opposite the "List" is a record of seven specimens taken "April 



