2i8 KINGSLEY. [Vol. VIII. 



lumen and with an external opening pear-shaped in outline, 

 narrower in front and wider behind. It is in fact enclosed by 

 two ridges, one on either side, while posteriorly it is without 

 distinct boundaries and passes directly into the ventral ecto- 

 derm. The lateral walls gradually unite in front {cf. Vol. VII, 

 Figs. 30, 31), and are at the same time added to behind. It 

 is by the continuation of this process that the stomodaeum is 

 invaginated and the mouth comes to occupy a position behind • 

 the first pair of appendages. Thus it will readily be seen that 

 with regard to Limulus, at least, Claus is wrong when he says 

 ('87, p. 129) that the preoral condition of the appendages is 

 "nicht ein Lagenwechsel des Mundes . . . sondern eine im 

 Laufe der Entwicklung vollzogene Aufwartsbewegung der 

 Gliedmassen mit entsprechenden Verschiebung der Ursprungs- 

 stelle des zugehorigen Nerven." It would seem probable that 

 the same conditions obtain in the Crustacea, but detailed ob- 

 servations are as yet lacking. 



At first the cells of the stomodaeum invaginated in this man- 

 ner form a low cubical epithelium, but they soon elongate and 

 assume the columnar character which is found in this region 

 in all the later stages. At an early date they also begin the 

 secretion of the chitinous cuticle. At the outset all of the 

 stomodseum is apparently formed by this invagination, and the 

 tube is straight between mouth and the inner end. Later it 

 begins to elongate by interstitial growth, and in this way a 

 flexure in the sagittal plane is produced {cf. Figs. 81, 82). 

 This flexure is also increased by the flattering of the em- 

 bryo. 



With the introduction of the flexure there begins a differ- 

 entiation of the stomodaeum, at first into an internal proven- 

 triculus (stomach of most authors) and an outer tube. Later, 

 the latter in turn is subdivided into buccal cavity and oesoph- 

 agus proper (Fig. 81) In the proventriculus there soon 

 develop longitudinal folds, and before the connection of stomo- 

 daeum with mesenteron is effected, the proventriculus has, 

 except in size, the characters which it has in the adult. 



After the epithelium of the midgut has been formed at 

 the anterior end, the connection between fore- and midgut is 



