1930] Subaptery and Aptery in Genus Monomorium 205 
the following description is offered. The specimens exam- 
ined are all from the collection of Dr. Wheeler, through 
whose kindness the writer is enabled to describe them. 
The subapterous female of this particular species meas- 
ures 6.5 mm., has well-developed ocelli, and its thorax 
(Fig. A), although somewhat reduced, is of the same gen- 
eral composition as its close relative, M. subapterum. The 
stumps of wings are present except on the hind right side, 
where the entire wing is retained. It is much reduced in 
size and may be considered as vestigial. The other wings 
have been lost by deflation. The structure of the pleural 
region of the thorax is not unlike that of other Myrmicinse, 
and since it is not the purpose of this paper to discuss 
the morphology of these forms, but rather to indicate the 
annectant stages between the alate and the apterous castes, 
a discussion of the different sclerites is omitted. The second 
stage (Fig. B) is one in which the hind wings have entirely 
disappeared, yet the stumps of the fore wings are present. 
The transition to this stage has been accompanied by a 
reduction in size of the thorax and by the fusion of the 
pleuron and notum in the regions formerly occupied by 
the hind wings. A further step in the series (Fig. C), 
indicated that the wings have totally disappeared, and the 
fhorax has become greatly reduced in size. Fig. D repre- 
sents another stage illustrating a simplification of structure 
and a reduction in size. Fig. E represents the true worker 
and is characterized by the presence of an enlarged pro- 
notum, which appears to be a fairly constant character of 
the worker caste among most genera of Myrmicinse. 
The evidence derived from the series of Pogonomyrmex 
and this series of Monomorium may have an important 
bearing on the question of the production of organic forms 
through continuous or saltatory variation. The gradation 
of the intermediate forms is so continuous that one is almost 
forced to accept the explanation of the production of organic 
forms through continuous variation as the more logical of 
the two. The appearance of intermediate forms would 
seem to suggest at once that the origin of castes could not 
have come about as- a saltatory variation or mutation. 
It is very possible that the explanation involving continu- 
ous variation may be incorrect, and one must turn to other 
