CONTROL OF HEAD-FORM IN PLAN ARIA 103 



In the experiments with cyanides and various narcotics the 

 pieces are kept in lots of fifty in corked 1 htre Erlenmeyer flasks 

 and the solution or water is renewed every forty-eight hours where 

 the length of time in the solution is more than this. It was 

 determined b}^ experiment that the confinement of fifty pieces 

 in well aerated water in such flasks is without appreciable effect 

 on head-frequency. The controls and experimental lots are 

 kept at the same temperature and under conditions otherwise 

 as nearly identical as possible, except as regards the factor to 

 be tested. The exact method of use of the reagent differs in 

 different cases: the whole animals may be placed in it immedi- 

 ately or some time after cutting. Pieces may be kept in the 

 solution only a few hours or during the whole process of recon- 

 stitution, two or three weeks, and of course much higher con- 

 centrations may be used for the shorter than for the longer 

 periods. Such details of experiment are stated in connection 

 with each series. 



II. THE DIFFERENT FORMS OF THE HEAD 



The different forms of head have been described elsewhere 

 (Child, '11a, 'lib, '15 a pp. 110-112, '15 b, pp. 106-107), but 

 their distinguishing characteristics are briefly stated here. 



The normal head is a head like that of the animal in nature, 

 with pointed anterior end, lateral cephaHc lobes and two dis- 

 tinct symmetrical eyes (figs. 8 and 9). 



The teratophthalmic head is one in which the eyes show some 

 departure from the norm. They may be unequal in size, asym- 

 metrical in position or, as in most cases, show various degrees 

 of fusion of the pigment cups and under certain conditions may 

 differ in number from the normal. Figure 1 shows a common 

 type of teratophthalmic head and figure 2 some of the eye forms. 

 The condition of the eyes is merely an index of the condition 

 of the cephalic gangha (Child and McKie, '11). In general 

 outline and in position of cephalic lobes the teratophthalmic 

 head is hke the normal (fig. 1). 



