596 Bashford Dean Memorial Volume 



veloped. But most noticeable in the dogfish is a profusion of long gill'filaments coming 

 out of slits 1-2-3, while shorter ones are to be seen in the spiracular cleft and the fifth 

 slit. There is no indication of such filaments in the 20'mm. Chlamydoselachus, although 

 the slits have apparently broken through. 



Two 25'MM. Specimens — Heads Only — Described by Ziegler and Brohmer 



In 1908, Paul von Rautenfeld brought to Germany from Japan a collection of 2;oologi' 

 cal material, among which were three embryos of the frilled shark — two of 25 mm. 

 without yolk sacs and one of 70 mm. with a yolk sac. These presently came to H. E. 

 Ziegler for study. He figured and described (1908) one 25'mm. head in both lateral and 

 ventral aspect. Then he cut sections of this and studied them as noted above. The 

 other 25--mm. embryo and the 70'mm. specimen on its yolk sac, briefly referred to else' 

 where, were turned over to his student, Brohmer. The latter deposited the larger embryo 

 in the museum at Jena, but figured and described the head of the 25'mm specimen in 

 dorsal aspect (1909). Then he sectioned it and studied it in comparison with Hke em- 

 bryonic material from other sharks.. 



Dean's embryos above were all portrayed in lateral aspect only. The head of 

 Ziegler's embryo was figured in lateral and ventral views and Brohmer 's of the same size 

 was portrayed in dorsal view. Since nearly all Dean's embryos figured are shown in all 

 three aspects dorsal, lateral and ventral — these figures will be studied in that order. For 

 this reason it has seemed well to begin consideration of the 25'mm. specimens by properly 

 combining and studying the figures of Brohmer and Ziegler. 



Head in Dorsal Aspect. — First let us consider Brohmer's figure (1909) of the head of 

 the 25-mm. embryo seen from above reproduced herein as Text'figure 27a. Here the 

 head seems to be pointed. The eyes are prominent, as are the spiracles. The gill-arches 

 stand out widely — the first at about right angles to the body, the other five being directed 

 obliquely backward. All have very short external gill-filaments. The pectoral fins show 

 the beginnings of the basal cartilages. The most striking thing shown in this embryo 

 is the transparent roof of the hindbrain — through which can be seen the floor with 

 its median groove. 



Ziegler (1908) figured the head of one of the 25-mm. embryos in both lateral and 

 ventral aspects (my Text-figure 27). I will first give Ziegler 's descriptions of his figures, 

 and will then call attention to particular points. Ziegler wrote as follows : 



Der weit geofFnete Mund ist jederseits von dem Kieferbogen begren2;t. Die Ober- 

 kieferwiilste sind gross und lassen vorn median zwischen sich noch eine Liicke, an welche sich 

 eine kleine mediane Rinne an der Unterseite des Vorderkopfes anschliesst. Auffallend ist die 

 Grosse des Spritzloches und die ausserordentliche Weite der ersten echten Kiemenspalte. 

 Die folgenden Kiemenspalten sind schmal und unter einander nicht viel verschieden. Bekannt- 

 lich gleicht Chlamydoselachus insofern dem Hexanchus, als 6 Kiemenspalten auf das Spritz- 

 loch folgen. 



Hinter der letzten Kiemenspalte liegt noch ein kleiner Wulst, welcher die Kiemenregion 

 abschliesst; an Fig. 1 wird er durch die letzte Kiemenplatte verdeckt. Dann folgt die vorder 

 Extremitat, sowie ventral der Nabelstrang. 



