4 ABNORMAL CONDITIONS OF THE AXIS. 



of the embryo the yelk is on its ventral surface, but soon the 

 left side turns towards the yelk. Transposition of the viscera, 

 as was long ago pointed out by Von Baer, probably arises from 

 this turn taking place in the opposite direction, so that the right 

 side of the embryo comes to lie upon the yelk. It is not a 

 little remarkable that so slight a deviation should be so very rare 

 and so frequently accompanied by grave malformations. In 

 cases of transposition there appears to be a strong tendency in 

 many organs to revert to their normal position ; thus transposi- 

 tion is frequently partial. In the Mollusca transposition occurs 

 commonly in some few genera, and has long been considered 

 as a variation ; one species of Whelk is constantly reversed. 



18. The trunk of a human foetus with complete transposition of 



all the viscera. The small intestines have been removed. 



Mus. Heaviside. 



19. An injected and dried preparation of the heart and large 



vessels, with some of the abdominal viscera of a human 

 adult, in which all the parts are transposed. The pre- 

 paration includes the stomach, liver, spleen, and caecum. 



Class II. DUPLICITY. 

 Subseries I. IN INVERTEBRATES. 



Subclass I. Dichotomy. 



20. An Earthworm with the posterior third of the body sym- 



metrically double. Presented by W. Clift, Esq., 1810. 



Subseries II. IN FISHES. 



Subclass II. Homologous union. 



21. Two specimens, each consisting of two newly hatched Trout 



united by the posterior portions of the ventral aspect. 

 The single yelk-sac is attached to the lower specimen, 

 showing their origin from a single yelk. 



Presented by the Duke of Wellington, 1870. 



22. Two small Sharks united in the same manner as the Trout 



