30 THE PINEAL ORGAN 



have to be carried out by alternate respiratory and suction movements. 

 In many cases, also, there are grave defects in the development of the 

 brain, and the young are apt to die suddenly in convulsions soon after 

 birth, as in cases of anencephaly. With regard to the possibility of a 

 cyclops possessing normal vision, we find that in nearly all the published 

 cases in which a dissection has been made of the median eye, the interior 

 of the eyeball is almost completely filled with choroid and no mention is 

 made of either retina or vitreous. Moreover, the lens has been found in 

 some instances to be double, or if single it has usually shown signs of its 

 composite nature. It is extremely improbable, therefore, that if it were 

 possible for a human cyclops to reach maturity, he would possess normal 

 vision. 



The cause of cyclopia and the frequently associated defect agnathia 

 has been investigated by many authors and experimental embryologists, 

 and numerous theories have been advanced in explanation of the defect. 

 The more important of the earlier contributions were summarized by 

 Schwalbe, who gives full references to the literature up to the year 1905. 

 Since this period the various theories with regard to the nature of cyclopia 

 and of the malformations which are usually associated with it have been 

 profoundly modified by the conception of the regulation of growth by the 

 action of an organizer — more particularly at centres of cell-proliferation 

 such as the " apical bud " of a growing stem or the " dorsal lip " of the 

 blastopore. Some of the more recent publications on the nature of 

 cyclopia are referred to in a paper which was published by us jointly in the 

 Journal of Anatomy (1920) on a " Cyclops Lamb (Cyclops rhinocephalus)." 

 In this communication we pointed out that a distinction may be drawn 

 between those cases of cyclopia which occur in primarily double-headed 

 monsters as the result of the fusion of the outer segments of eyes derived 

 from two heads, and those which occur in single-headed monsters, the 

 cyclops eye being due in these cases to the fusion of the temporal halves 

 of the eyes belonging to one head in which the central region of the head, 

 including the nasal halves of the two eyes, has failed to develop. As a type 

 of the former we may select an example of the well-known class Cephalo- 

 thoracopagus monosymmetros, in which the two heads are united in such 

 a way that two " secondary faces " are formed (Fig. 23, A and B). One 

 of these faces may be regarded as looking forwards and the other back- 

 wards. The secondary face in A is apparently complete, whereas the 

 secondary face on the opposite side of the double-head seen in B is in- 

 complete, there being neither nose nor mouth, and there being but one 

 palpebral aperture, p.ap., in the situation of a cyclops eye which is hidden 

 from view by the fusion of the outer segments of upper and lower eyelids 

 belonging to the two heads. The difference in the two heads is accounted 



