114 ILLINOIS STATE ACADEMY OF SCIENCE 



of one of the embryos has fused with the right organ of 

 the other embryo. Accordingly, the normal eyes and ears 

 are to be interpreted as the right and left organs of the 

 two primitive embryonic stages. 



Two trunks, joined to each other in the mid-ventral 

 thoracic regions, are attached to the posterior lat- 

 eral angles of the head. These trunks are of unequal 

 size. The larger is on the right side, considered from 

 the standpoint of the head, and measures 25 cm. from 

 crown to rump; while the smaller animal, similar on 

 the left side, has a corresponding measurement of but 

 18 cm. The bodies are joined as far back as the unpaired 

 umbilical cord, which contains upon examination two 

 arteries and two veins. There are eight legs, completely 

 developed, which occupy proper positions upon their re- 

 spective girdles. The smaller animal is devoid of tail as 

 well as external genitalia and rectal openings ; while the 

 larger one possesses all these structures and is of the 

 female sex. 



INTERNAL ANATOMY 



The metacoeles of the two bodies are continuous, so 

 that the peritoneum of the one continues directly into 

 that of the other; thus but a single metacoele may be 

 identified. The common viscera lies almost entirely in 

 that portion of the metacoele which lies within the larger 

 animal ; although a relatively small part does extend over 

 into that portion of the metacoele in the smaller pig. A 

 fused diaphragm, resulting from the greatly modified 

 development, cuts off two anterior pleural regions from 

 this common metacoele, and extending back along the 

 dorsal surface of each body reaches to a line just anterior 

 to the paired kidneys. 



THE ALIMENTARY TRACT 



The buccal cavity and the pharynx are entirely nor- 

 mal, as well as those structures within them. From the 

 pharynx two larynges with normal epiglottes extend pos- 

 teriorly, and between them, definitely opening from the 

 more ventral larynx, is the single oesophagus which con- 

 tinues posteriorly between the two tracheae into the me- 

 tacoele. 



