430 Harris Hawthorne Wilder 



and post-uterine life, he, as well as others, emphasizes a point of little 

 importance and ignores one that is fundamental. The time of birth 

 is relative, and is merely an incident in the life of the young organism. 

 A similar mechanical injury happening to a marsupial and to a placental 

 mammal in precisely the same stage of development might cause the 

 latter to be classed as a monster, the former as a cripple! The other 

 fault, that of placing in one category diplopagi and fetal amputations 

 has already been sufficiently commented upon. 



Following this definition comes a concise and valuable review of the 

 previous work on teratolog}% and a discussion of the principles under- 

 lying the formation of monsters, a discussion in which the author is 

 hampered by his attempt to class all monsters together under a single 

 term. In his discussion of causes he leaves the Diplopagi for later 

 treatment in the second part of the work, and considers here the follow- 

 ing as possible causes of monstrosity: mechanical causes, psychic causes, 

 changes of temperature, lack of oxygen, chemical influences (mainly 

 poisons), changes in osmosis, fetal disease, and deformities due to the 

 amnion. Psychic causes, i. e., maternal impressions, he naturally dis- 

 misses as improbable, and lays great stress on causes due to mechanical 

 derangement of amniotic elements. In all this part of the work the 

 author shows the interest of a trained pathologist and the cases referred 

 to are mainly pathological. As the discussion of double monsters is 

 postponed until later, the only cosmobia to be considered here are those 

 that are less than a single individual, and of these Cyclopia is the only 

 type treated. This he is disposed to view as the result of abnormal 

 pressure exerted upon the very young embryo {i. e., a secondary and 

 mechanical cause), but he is especially careful to point out the fact that 

 this cause does not make the separate lateral parts grow together, but 

 prevents them from developing at all; "eine anscheinende Verwachsung 

 ist sehr haufig eine unvollkommene Trennung." 



Schwalbe's second part, which appeared in 1907, is wholly devoted 

 to the discussion of Diplopagi and will long be of the utmost importance 

 to students of that branch of teratology. In this, aside from a volumi- 

 nous descriptive part, he discusses the causes of double formations, and 

 includes in this a treatment of the various theories that have been sug- 

 gested in the past. His own opinion, which is cautiously stated, may 

 be tabulated as follows : — 



{a) In the case of most double monsters the time for the action of 

 the cause closes with gastrulation. 



