This paper is a huge work on comparison the morphology of head structures in the larvae and adults of the lower Diptera. The study is descriptive and it is extremely complete. The authors used mostly a many data sets from own previous papers and other authors. The original achievement of this paper is description several new characters documented in the figures (images), which quality are very good. As a whole this paper is an important contribution to evolution of lower Diptera. It seems to me also, generally, is very well written and it represent a valuable review on the subject (but I’m not a specialist in dipteran field). This exhaustive review will be of utility for other researchers and for future phylogenetic studies on the group.
Materials and Methods, and References are correctly and exhaustive prepared. Generally the all paper is precisely formed.
Overall, as a reviewer I have no reason to suggest any major changes.
1. The author discuss the morphological characters in a phylogenetic perspective. This parts, in my opinion, is not very clear. The authors should consider, in all presented trees also the outgroups, not only in the fig 1C. These outgroups are mentioned in the table 1 and 2 and in the appendix 1 and 2, but they are not included in the cladograms.
Essentially in the Tree1 A and B the outgroups are not analyzed, so they arrangement and relationships of the taxa are not compatibility with C.
2. In the figure 2 (page 6) the "potential apomorphies" should be evaluated as the synapomorphies and autapomorphies for the taxa.
3. The groundplan is made incomprehensible - say clearly what do you understand under"groundplan" (GP) of Diptera head. Generally, GP includes the total of plesiomorphic characters states observed among the species of a group but also the sum of its autapomorphies (of Diptera = synapomorphies of all lower dipteran families) as well the sum of inclusive apomorphic homoplasies shared by all the group.
In present paper the "apomorphy groundplan" of head is presented as separate parts for larvae and adults and several apomorphic characters are mentioned in different sentences/lines. It seems necessary to summarized this groundplan e.g., in the table, the more so that the aim of this paper is indicated the "reconstruction of the ordinal groundplan"