DETAILS OF LATER EMBRYO. 109 



shark-like, so also are its early rostral cartilages. In Chimaera, on the other hand, 

 the developmental processes, evidently abbreviated, produce larger orbits, larger 

 auditory organs (from this is due the broadening of the skull noted above), coales- 

 cence of foramina, and altogether a more mature modeling of the head.* In this 

 form, moreover, we find in the hyoid arch more perfectly developed ceratohyal and 

 greatly reduced pharyngobranchial elements. It follows, I conclude, in view of 

 these and other evident specializations^ that one can not reverse the order of 

 comparison and regard Chimaera as resembling the" more closely the ancestral type 

 from which in turn Callorhynchus and sharks developed. 



COMPARISONS WITH OTHER CHIM/EROIDS. 



Before concluding the account of the later embryonic stages of Chimssroid, 

 which we have hitherto based upon C. colliei, reference should be made to the 

 conditions known in other genera and species. 



In Callorhynchus. Schauinsland has already given many observations upon 

 the young of Callorhynchus. It appears from his figures that there are little 

 outward differences in the development of stages corresponding to those of plate 

 vii, fig. 45, of Chimara colliei, and that of Callorhynchus in Schauinsland's Taf. 

 xin, fig. 105. Also there are but minor differences between the present plate vii, 

 fig. 42, and Schauinsland's Taf. xm, fig. 98. We may thus compare also the 

 present plate vn, fig. 45, with Taf. xiv, fig. 107, also plate vn, fig. 43*, with Taf. 

 xiv, fig. 106. In a later stage, contrasting Chimaera in plate vin, fig. 49, with 

 Schauinsland's Taf. xv, figs. 116 and 117, we can not fail to note the more shark- 

 like conditions in the Australian species, and this is even more evident if we contrast 

 the still later stage of C. colliei given in the present plate ix, fig. 50, with Schau- 

 insland's Taf. xv, fig. 121. Observe in this connection the less tapering tail of 

 Callorhynchus, a more distinct second dorsal fin and the early appearance of the 

 row of dorsal scales which suggest closely the conditions shown in Scyllium by Paul 

 Meyer. 



In referring to the latest embryonic stages in Callorhynchus, outline drawings 

 may be given of specimens preserved in the department of ichthyology in the 

 British Museum, figs. 86-88, and in the Copenhagen Museum, fig. 89. % And these 

 may in turn be compared with the outline of the young Callorhynchus, fig. 85, 

 figured by Parker and Haswell in their Text-book of Zoology. An examination of 

 these figures shows that the absorption of the yolk-sac takes place, as one would 

 expect, while the embryo is still inclosed within the capsule. In fig. 85 the yolk- 

 sac is of irregular shape, rather large, and the embryo still retains its external gills. 

 In figure 86 the sac, still large, is somewhat bilobed, a condition which becomes 



*Cf. also in this connection the more advanced condition of the mixipterygia in Chimaera (plate ix, fig. sof, and 

 Schauinsland's Taf. xvi, fig. 120). 



fin morphological regards cf. the reduction of dermal defenses, great size of head, reduction of caudal region, differ- 

 entiation of dorsal fin, specialization of clasping organs, modification of brain. 



JFor the privilege of examining these valuable specimens the writer is indebted to Mr. Boulenger and to 

 Dr. Winge. 



