Phocæiia eommimi8, Lesson. 



Pl. IV. 



O, 



n account of tlie frequent occurrence of tlie conniion Porpoise on all European coasts, it has Ijeen employed almost as 

 a paradigm when the anatomy of the Cetacea has been in question; and from the time wlien Thomas Bartholin (14) dissected 

 the gravid Porpoise in the presence of the Dano-Norwegian king, Frederick III, until our own day, scarcely any Cetacean 

 has been so much examined. In this way the Phocæna has served as the subject for Rapp's anatomical description 1.37) of 

 the Cetacean type, while its external form and occurence are treated of by many older naturalists. Kiik ent hal (.58, II Theil) 

 has lately given descriptions of the external form of quite small embryos; Klaatsch (ho) has described its ffetal membranes; 

 James Grieg (8.3) with splendid material for his basis, has treated thoroughly the question of the duration of its gravidity; 

 wliile P. .T. Tan Beneden, on a ground-work of old and new observations, has given us its "histoire naturelle". 



While I pass over the rather diffuse literature of this species and direct attention on that point to the well-known 

 works of Rapp. van Beneden (84), Lilljeborg (72) and others, Iwill, in addition to the description of the small embryonic forms 

 of Lagenorhynchus acutus, Gray, supplement our knowledge of the earlier stages of the Odontoceti's developement, by a 

 description of an embryo of this species 7 millim. in length, another 17, and a third 18 millim. in length. The first of these, the 

 7 millim. long fætus, proved to be well preserved as far as its external form was concerned, and rei)resents not only the 

 smallest specimen, but also the earliest stage of developement hitherto described of any Cetacean. The 7 millim. and the 17 

 millim. long embryos were taken by Mr. Bistrup, Sukkertoppen, Greenland, in 1892.') 



I. The smallest Phocæna embryo, preserved in alcohol, was enclosed in a double amniotic bag, while the long 

 chorion was open. The length, measured from the flexure of the neck to that of the tail, was 6V2 or 7 millim. 



On opening the amnion and stripping the embryo of it. the latter proved to be in an exceedingly well-preserved condition. 



The embryo (Fl. IV, figs. 1 and 6 — 12) resembles, as regards its degree of developement, a human embryo of 

 about 4 or .5 weeks. In addition to the marked fretal flexures, this stage of developement is distinguished by the pronounced 

 visceral arches with visceral grooves, the incipient olfactory depressions, the but slightly differentiated eye developement. the 

 long, bent tail reaching to the facial region, and the formation of the extremities, the distinct bud-like rudiments of 

 hind-extremities being undoubtedly among the most interesting conditions of external form in the developement of the Cetacea. 



The foetal flexures in this small fætus are as marked as those in an embryo rabbit of 10 or 12 days, or an embryo 

 dog of 2.5 days. Thus the flexures of the crown of the head and the back of the neck are each bent in a right angle. The 

 bend of the tail describes an arc of 180''. The neck and chest regions lie close to one another, and the relatively very long, 

 cylindrical tail extends as far as to the anterior part of the head. 



The head, measured from the flexure of the crown of the head to the middle of the neck flexure, is about 3\'i 

 millim. in length, while the distance from the ventral surface of the facial region to the crown of the head is about 2V2 

 millim. The thickness, i. e. from side to side, is about 2V 3 millim. 



The upper surface of the head presents no even surfaces. Through the thin, transparent skin covering, in the 

 region between the crown of the head and the flexure of the neck, the relatively large fovea rhomboidalis (PI. IV, fig. 9) 

 is visible. The flexure of the crown of the head and the region in front of it are inclosed in an elongated oval arch that 

 is connected with the mesencephalic vesicle, and before this on the front of the head, may be distinguished under the integuments, 



1) These two eiubi-yos and a small Phoca gronlandica fætus were sent, togetlier witli several other zoological specimens, to Prof. R. 

 Collett, who transmitted the embryos to the Zootomical JIuseum. Dr. .T. Hjort, the keeper of that museum, gave tliem to me for examination, for 

 wliich act, I offer him my best thanks, 



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