598 Bashford Dean Memorial Volume 



Scammon's drawing of his 24.7'nim. Squalus is in full-length lateral aspect only. 

 When Ziegler's drawing of the lateral head of his 25'mm. specimen is compared with the 

 head only of Scammon's Squalus, it is at once seen that the latter is more developed. Its 

 gill'arches are more finished and are filled with a profusion of long external filaments. The 

 spiracle is closed off and is also filled with filaments. Its pectoral fin, however, is in about 

 the same stage of development as that of Chlamydoselachus. 



Nishikawa's 32-mm. Embryo — Head Only 



The next stage called for in Dean's "List of Figures" for the development of Chlamy- 

 doselachus, is noted thus "Emb. of mm. 32 — general view 2 figs.; head 3 pos'ns." No 

 "general view 2 figs." can be found, but there are views of the head only, in dorsal, 

 lateral, and ventral positions. These are reproduced as Figures 19, 20 and 21, plate II. 

 But before describing them, I wish to set forth here a very interesting matter. Earlier in 

 this article, I have expressed the belief that all Nishikawa's materials were turned over to 

 Dean while he was working at Misaki and Tokyo. Nishikawa's brief article had been 

 published in 1898 and in it he had figured the head of a 32'mm. embryo (his smallest 

 specimen) in dorsal, lateral and ventral aspects. Dean had no specimens of his own be- 

 tween 20 and 34 mm. To lessen this gap in Dean's series of drawings showing the pro- 

 gressive development of the frilled shark, the figures of the head of Nishikawa's 32-mm. 

 embryo were redrawn at the University (by Kuwabara ?) for reproduction by lithog- 

 raphy. I have compared the two sets of three figures minutely and can affirm that they 

 are identical. 



But the reader may be wondering why Dean had Nishikawa's figures copied instead 

 of having drawings made de novo, and why no full-length drawings are available as called 

 for. The answer is to be found in Nishikawa's article (1898, pp. 98-99) wherein he 

 figures diagrammatically and describes sections of the head of this embryo — it had been 

 cut into sections in 1896. 



Head in Dorsal Aspect. — The head of the 32-mm. embryo is seen from above in 

 Figure 19, plate II. This head must be contrasted with that of the 25-mm. embryo por- 

 trayed in Text-figure 27a. The head in each figure is pointed. The curious outline on 

 the head in Figure 19, plate II, is probably caused by the shrinking of the skin on the 

 embryonic skull. In the 25-nmi. head as drawn, the tissues are transparent and allow one 

 to see the floor of the brain cavity. The 32-mm. head has the openings of the endolym- 

 phatic ducts which are lacking in the 25-mm. head. The former has the large spiracles 

 seemingly placed higher on the head than those of the younger embryo. There are short 

 filaments on both sides of the widely spread gill-arches of each head. The rudimentary 

 pectoral fins are about in like stages of development in each embryo. On the whole the 

 head of the 32-mm. specimen looks older and more perfected. 



Head in Lateral View. — It is to be regretted that no full-length drawing of the 32- 

 mm. embryo in lateral aspect is available for comparison with that of the 20-mm. specimen 

 (Figure 18, plate II). One wishes to see what differentiation has taken place in body and 

 tail as well as in the head. However, Figure 20, plate II, shows some interesting struc- 



