Geophilus, at the time of birth, has a rounded form like that of the Chilognatha.
The young of Lithobius is born with only six pairs of limbs.
General observation on the homologies of the appendages of Myriapoda.
The chief difficulty in this connection is the homology of the third pair of post-oral appendages.
In adult Chilognatha there is present behind the mandibles a four-lobed plate, which is usually regarded as representing two pairs of appendages, viz. the first and second pairs of maxillæ of Insects. Metschnikoff’s observations seem however to shew that this plate represents but a single pair of appendages, which clearly corresponds with the first pair of maxillæ in Insects. The pair of appendages behind this plate is ambulatory, but turned towards the head; it is in the embryo the foremost of the three functional pairs of legs with which the larva is born. Is it equivalent to the second pair of maxillæ of Insects or to the first pair of limbs of Insects? In favour of the former view is the fact (1) that in embryo Insects the second pair of maxillæ sometimes resembles the limbs rather than the jaws, so that it might be supposed that in Chilognatha a primitive ambulatory condition of the third pair of appendages has been retained; (2) that the disappearance of a pair of appendages would have to be postulated if the second alternative is adopted, and that if Insects are descended from forms related to the Myriapods it is surprising to find a pair of appendages always present in the former, absent in the latter. The arguments which can be urged for the opposite view do not appear to me to have much weight, so that the homology of the appendages in question with the second pair of maxillæ may be provisionally assumed.
The third pair of post-oral appendages of the Chilopoda may probably also be assumed to be equivalent to the second pair of maxillæ; though they are limb-like and not connected with the head. The subjoined table shews the probable homologies of the appendages.
| Chilognatha (Strongylosoma at time of birth). | Chilopoda (Scolopendra adult). | |
| Pre-oral region. | Antennæ. | Antennæ. |
| 1st Post-oral segment. | Mandibles. | Mandibles. |
| 2nd Post-oral segment. | Maxillæ 1. (Four-lobed plate in adult, but a simple pair of appendages in embryo). | Maxillæ 1. (Palp and bilobed median process). |
| 3rd Post-oral segment. (probably equivalent to segment bearing 2nd pair of maxillæ in Insects). | 1st pair of ambulatory limbs. | Limb-like appendages with basal parts in contact. |
| 4th Post-oral segment. | (?) Apodous. | Poison claws. |
| 5th Post-oral segment. | 2nd pair of ambulatory limbs. | 1st pair of ambulatory limbs. |
| 6th Post-oral segment. | 3rd pair of ambulatory limbs. | 2nd pair of ambulatory limbs. |
| 7th Post-oral segment. | 4th and 5th pair of ambulatory limbs. | 3rd pair of ambulatory limbs. |
| 8th Post-oral segment. | 6th pair of ambulatory limbs. | 4th pair of ambulatory limbs. |
| 9th Post-oral segment. | Apodous. | 5th pair of ambulatory limbs. |
| 10th Post-oral segment. | " (last segment in embryo). | 6th pair of ambulatory limbs. |
The germinal layers and formation of organs.
The development of the organs of the Myriapoda, and the origin of the germinal layers, are very imperfectly known: Myriapoda appear however to be closely similar to Insects in this part of their development, and the general question of the layers will be treated more fully in connection with that group.
The greater part of the blastoderm gives rise to the epiblast, which furnishes the skin, nervous system, tracheal system, and the stomodæum and proctodæum.