412 Harris Hawthorne Wilder 



one of B. The outer eyes of the components were normally placed and 

 the entire outer side of each head, with its associated snout, was normally 

 proportioned and appeared precisely like the corresponding side of a per- 

 fectly normal embryo. 



For ease in imbedding and sectioning the embryo was divided trans- 

 versely at about the middle of the belly into an anterior and a posterior 

 half. The sections were each 20 microns in thickness and the entire series 

 filled 43 slides of large size, and included 920 sections. From these, 

 aside from general study. I have already constructed three wax models, 

 one of the brain, together with the eyes and some of the more obvious 

 cranial nerves, one of the skeletal elements of the head, and one of the two 

 inner eyes with their associated nerves and muscles. Of these the two 

 first were on a rather small scale (X 12), and the third was constructed of 

 twice this size (X 25). All three of these, down to the smallest details, 

 are fully as symmetrical as the corresponding parts of a normal head, 

 and the one or two slight deviations are of the same nature as those 

 found in the two sides of any individual. 



Every section in this series, allowing for the mechanical defects pres- 

 ent in all series, is a symmetrical one, and nowhere is there a suggestion 

 of tissue that is in any sense pathological or abnormal. There is not 

 even an area of dense connective tissue due to the crowding of parts, 

 such as almost always occurs in places along the median line of doul)le 

 monsters when more fully grown, and to one looking over the series the 

 impression given is that of normally developing parts, in perfect harmony 

 x^'ith one another, as in any other organism. In working over this 

 series, with nothing to suggest the abnormal, one comes to forget that 

 it is even unusual, until finally it seems as natural to see in a given section 

 two brains or two sets of nasal cartilages, symmetrically placed, as it is 

 to find two eyes or two ears. To give the reader some suggestion of this 

 impression as well as to form an introduction to the description of the 

 monster in question, I present here drawings of two sections of the 

 series, taken from the double region, the one through the median eyes, 

 the other at the level of the two lateral eyes and cutting across the two 

 snouts. The several slight departures from perfect symmetry are due, 

 as in any series, to slight variations in the level of the two sides and to 

 obliquity in the plane of section. 



In the first of these sections are seen the two median eyes, the two 

 fore-brains and a single hind-brain of abnormal width, partly double 

 ventrally. Both fore-brains are cut a little obliquely, owing to the 



