456 Mabel Bishop 



component A is necessary to complete the symmetrical condition that I 

 believe existed at an earlier period in the development of this Teras. 

 This branch is indicated in the plate by a dotted line [Plate V, x]. 

 Some secondary variations are present, for example, the origin of both 

 Unguals of component B from one external carotid, instead of one lingual 

 from each, and the loss of one lingual artery by component A, but these 

 are of minor importance and are the results of continual solutions of 

 physiological problems during the entire development of the organism. 



While it cannot be denied that this creature is "unusual," it is obvious, 

 nevertheless, that it is perfectly symmetrical, that Avith the exception of 

 the everted brain it is in no sense pathological, but that on the contrary 

 it has developed according to the laws of an orderly living being, and 

 therefore has a right to the title "Cosmobion," and a definite place in the 

 cosmobiotic series with which this investigation is concerned. 



As the doubling in the dicephalus group increases, so also the diver- 

 gence of the two components increases. This is well illustrated by the 

 two-headed lamb (Teras XV), which represents the next stage in the 

 series. In this specimen the heads are separate as far back as the occipi- 

 tal region. Each head has its normal parts and organs, e. g., two eyes, two 

 ears normally placed and normally developed. Obviously, then, the 

 doubling has progressed more posteriorly than in Teras XII, The follow- 

 ing description and comparison will show that the blood vessels have per- 

 fectly reflected these other anatomical changes. 



The heart of the dicephalous lamb is single, and fully three times the 

 size of that of the cosmobiotic pig, but is proportionate to the size of the 

 lamb. Its size may be easily approximated by the following measure- 

 ments taken along the same axes as in the double pig: — the longest 

 lateral line measures 6 cm., its transverse diameter across the anterior 

 surface is 5 cm.'^ In shape the heart of Teras XV is identical with that 

 of a normal lamb, and may be said to be shaped like an inverted pear, 

 but it differs from that of a pig, the heart of which is roughly acorn- 

 shaped. It is more elongated and pointed than a pig's heart, its posterior 

 face is slightly more concave, its right face is less bulging, and it has 

 not the appearance of having two apices that is so conspicuous in a pig's 

 heart. In both, the auricular appendages are rather flat. The heart 

 of the double lamb extends from the first rib to the fifth, which by com- 



'It should be mentioned here that in all the terata the measurements of 

 the heart, and its position in the thoracic cavity, were taken with the 

 specimen in a dorso-cumbent position and after long preservation in alcohol. 



