114 HORTENSK BUTLER. 



In the drawing made from the embryonic labium (PI. V, Fig. 13) 

 it will be observed that the development of the ligula (median lobe) 

 is very imperfect in comparison with that of the lateral lobes. In 

 the median cleft is a double basal series of teeth representing [)roba- 

 l)ly the inner laminae of Gerstaecker, with the lobe abov'e terminates 

 an important second series, representing probably the outer laminae. 

 This is probably another case of retarded development. In the lat- 

 eral lobe the movable hook is already well developed and separated 

 from the remaining parts ; the teeth are developed on the distal mar- 

 gin and to a less extent ou the inner margin ; the one at the end is 

 already differentiated as end hook. In the earliest of the nymphal 

 stages (PI. Ill, Fig. 1), the lateral lobes are separated by a low broad 

 ligida which has developed extraordinarily and which shows a trace 

 of a cleft in the middle. On either side of this cleft are two teeth, 

 the precursors of those lobes which in the full grown nymph extend 

 across the entire width of the mentum. The suture between the 

 ligula and the mentum (possibly, between inner and outer laminae: 

 its relation to these as shown in the earlier stages has not been fully 

 traced), which in nymphs has hitherto been entirely overlooked, ap- 

 pears as a transverse line with a pair of minute teeth at its distal 

 border. The position of the teeth on the lateral lobe is nuich 

 changed, owing perhaps to lateral expansion, the end hook is less 

 evident, but the development of the other teeth is about the same as 

 in the previous stage. 



In the next stage (PI. Ill, Fig. 2), after the second moult, a well 

 developed seta is observed on the lateral lobe and the beginning of 

 one on the movable hook, one is also present on either side of the 

 mentum, but this last is not included in the figure. The number of 

 teeth on the inner edge of the lateral lobe vhas increased, while 

 among those on the end, the one which later forms the end hook is 

 conspicuous by its size, and is already divided from the others by an 

 oblique cleft. The number of teeth on the ligula has increased and 

 the cleft is deepened, while a pronounced tooth has developed on the 

 sutural line before mentioned. 



In the third stage (PI. Ill, Fig. 3) the seta on the movable hook 

 has attained its full development, the cleft between the end hook 

 and the remaining teeth has become more marked, while the num- 

 ber of teeth on the ligula is still further increased, and the edge of 

 the ligula on either side of the cleft has become slightly elevated. 



