JO CYCLOPIA IN THE HUMAN EMBRYO. 



embryo. It has frequently been noticed that tadpoles whose growth has been 

 arrested develop stubby or club tails and fins a condition which corresponds 

 well with club-shaped extremities in man. Our collection contains 18 embryos 

 with deformed legs and feet, with catalogue numbers less than 400, ranging from 

 the very earliest period until the fetus is well formed. The leg-buds are irregular 

 in shape and are filled with condensed mesenchyme; sometimes they are stubby 

 on one side of the body and normal on the other. The study of the larger embryos 

 shows that there is a variety of inflammation of the tissues which is especially well 

 marked in the tendons and around the cartilages. In general this condition may 

 be accounted for by an arrest of development due to impaired nutrition. At any 

 rate, embryos that are not developing well experimental larvae and human 

 embryos with other malformations often have club-shaped arms, legs, fins, or tails. 



The inference to be drawn from the above summary is that after the eyes 

 have become well formed they do not pass out to the side of the head as in normal 

 development, but approach each other and more or less unite, and thus form 

 cyclopia. Recent embryological studies of Stockard and of Spemann show con- 

 clusively that this view can not be correct, for it is found that the cyclopean con- 

 dition can be followed back through earlier and earlier embryos, and that all 

 varieties of cyclopia are present while the eyes are still firmly attached to the 

 brain. It is now maintained by Stockard that, from its very beginning, the eye 

 primordium is in the midventral line of the brain, and that in cyclopean embryos 

 there is an arrest of its development, the eye remaining median or dividing in part, 

 forming the hourglass-shaped cyclopean eye with two lenses, etc. This view is 

 combated more or less by Spemann; but I must confess that it is difficult for me 

 clearly to understand his view as given in his various papers. 



Through his well-known magnesium experiments, Stockard has been able to 

 procure an abundance of material for the study of the early development of 

 cyclopia. He proves first of all that the condition of cyclopia is present in the 

 earliest stages in which it would be possible to recognize it. At no stage are there 

 two normal eyes which subsequently blend to form a single eye. The cyclopean 

 condition is present in the eyes while they are still closely attached to the brain. 

 Stockard observes, secondly, that the cyclopean eye is rarely equal in extent and 

 size to the sum of two normal eyes combined. A cyclopean eye is, as a rule, very 

 slightly if any larger than one normal lateral eye, and in fact it is often much 

 reduced or actually minute in size as compared with a normal eye. According to 

 Stockard, this fact indicates most decidedly that the eye material, as such, has 

 been injured or arrested in development and differentiation. He believes that we 

 are scarcely warranted in assuming, as have various authors at different times, 

 that cyclopia is due to a fusion of the eyes after they have arisen from the brain 

 and that the earlier in development the fusion occurs the more intimately asso- 

 ciated the two eye components become. This view, according to Stockard, has 

 been proved incorrect by actual observation on cyclopean monsters, where it is 

 found that the cyclopean condition of the eye whether large and hourglass- 

 shaped or of small size resembling a normal eye is present from the earliest 



