BRAINS OF THREE GENERA OF ANTS 555 



nificant in the male. While, therefore, the male brain in all these 

 species, apart from the huge development of its optic ganglia and stem- 

 matal nerves, is manifestly deficient, I doubt whether we are justified 

 in regarding the brain of the female as being inferior to that of the 

 worker. It is true that the worker brain is relatively larger, notwith- 

 standing the smaller eyes and stemmata, or the complete absence of 

 the latter, but I would interpret this greater volume as an embryonic 

 character. The worker is, in a sense, an arrested, neotenic or more 

 immature form of the female 



The queen brain seems to me to represent the generalized 

 type from which the worker caste has departed, and, while some 

 queens are notably degenerate in brain structure, others have 

 remained in a far more generalized condition, for example, the 

 queen of Lasius niger. If we select as a standard the degree of 

 development of (1) the optic apparatus, including the eyes and 

 optic lobes, (2) the mushroom bodies; and compare the castes of 

 the three genera under consideration with the queen of Lasius 

 niger, we shall obtain evidence of divergence from this type in 

 the two opposite directions of increase, and of reduction of parts, 

 or degeneration. From this comparative study (figs. 1-9) two facts 

 are worthy of note: (1) the Lasius queen has a more highly 

 developed, generalized type of brain than either of the queens of 

 Camponotus or Formica, (2) the queen brain in its most highly 

 developed, typical condition, as in Lasius niger, is superior to 

 and more highly developed than that of the worker. Therefore, 

 the conclusion is justified that the queen brain is the primitive 

 type from which by degeneration and specialization of structure 

 the worker brain has been derived. 



If the cause of the reduction or degeneration noted in the 

 brains of the queens of Camponotus pennsylvanicus and Formica 

 schaufussi is sought, may it not be found in the habits of these 

 queens? In a footnote to page 57, Wheeler ('10) states that the 

 queen of Lasius fuhginosus, described by Forel as possessing a 

 brain inferior to that of the worker, is but little larger than the 

 worker, and is probably a temporary parasite. This is evidently 

 a case where habit and structure are related. The male brain 

 is another example of the inter-relation of habit and structure, 

 since the great development of the compound eyes and optic 

 lobes may be attributed to the need to discern and follow the 



