NOTES ON THE DEVELOPMENT OF THE ARANEINA. 189 
In the Tracheata the mesenteron is always considerable, 
and the proctodseura is always short. The derivation of the 
Malpighian bodies from the proctodseum is common to 
most Tracheata. Such organs are not found in the 
Crustacea. 
With reference to other points in my investigations, the 
evidence which I have got that the chelicerae are true post- 
oral appendages supplied in the embryo from a distinct 
postoral ganglion, confirms the conclusions of most previous 
investigators, and shows that these appendages are equivalent 
to the mandibles, or possibly the first pair of maxilla of 
other Tracheata. The invagination, which I have found, of 
part of a groove of epiblast in the formation of the supra- 
oesophageal ganglia is of interest, owing to the wide exten- 
sion of a similar occurrence amongst the Tracheata. 
The wide divarication of the ventral nerve cords in the 
embryo renders it easy to prove that there is no median in- 
vagination of epiblast between them, and supports Kleinen- 
berg^s observations on Lumbricus as to the absence of this 
invagination. I have further satisfied myself as to the 
absence of such an invagination in Peripatus. It is probable 
that Hatschek and other observers who have followed him 
are mistaken in affirming the existence of such an invagina- 
tion in either the Chaetopoda or the Arthropoda. 
The observations recorded in this paper on the yolk cells 
and their derivations are, on the whole, in close harmony 
with the observations of Dohrn, Bobretsky, and Graber, on 
Insects. They show, however, that the first formed meso- 
blastic plate does not give rise to the whole of the mesoblast, 
but that during the whole of embryonic life the mesoblast 
continues to receive accessions of cells derived from the cells 
of the yolk. 
Araneina, 
1. Balbiani^ “Memoire sur le Developpement des Araneides,” ‘Ann. 
Sci. Nat.,’ series v, vol. xvii, 1873. 
2. J. Barrois^ “ Recherches s. 1. Developpement des Araignees,” 
‘ Journal de 1. Anat. e. de la Physiol.,’ 1878. 
3. E. Claparede, ‘ Recherches s. I’Evolution des Araignees,’ Utrecht, 
4. Ilerold, ‘De Generatione Araniorum in Ovo,’ Marburg, 1824. 
5. II. Ludwig, “ Ueb. d. Bildung des Blastoderm,” bie d. Spinnea, 
‘ Zeit. f. wiss. Zool.,’vol. xxvi, 1876, 
