ATAVISM OR REVERSION. 141 
thalmite was exopoditic, whilst the inner portion, which 
furnished the antenniform process, was endopoditic in 
character. 
The interest of this specimen lies in the fact that it is 
exactly analogous to the conversion of an element of a 
| flower, say a stamen, into a leaf. Although I have made 
a wide search, nothing in any way comparable to this 
specimen can be found recorded in zoological literature, 
| but there can be little doubt that such cases occur if we 
- would watch for them. One would also imagine that 
similar malformation must occasionally occur in the 
appendages of insects, but thus far my inquiries have 
not had any material result. 
From organs we turn our attention to tissues, and 
examine some specimens illustrating the reversion of 
mucous membrane to skin. 
The exterior of our bodies is covered by a membrane 
called skin, which differs in many points from that 
lining the internal cavities—the mouth, stomach, and 
intestines — and known as mucous membrane. The 
contrast between skin and mucous membrane is well 
illustrated in the case of the conjunctiva, the delicate, 
sensitive membrane covering the eyeball and ocular 
aspect of the eyelids. The conjunctiva is really modified 
skin, and not infrequently declares its ancestry by 
reverting to its original form. Indeed, it is no unusual 
event to find a patch of hair-covered skin growing upon 
the ocular conjunctiva. Such cases are far from rare. 
Mr. T. Collins is of opinion that about twelve cases of 
this abnormality are seen annually at the Ophthalmic 
Hospital, Moorfields. These dermoid patches are most 
