The differences between the Decapods and Isopods in the development of the mesenteron are not inconsiderable, but they are probably to be explained by the relatively larger amount of food-yolk in the latter forms. The solid yolk in the Isopods on this view represents the primitive mesenteron of Decapods after the yolk has been absorbed by the hypoblast cells. Starting from this standpoint we find that in both groups the lateral parts of the mesenteron become the liver. In Decapods the middle part becomes directly converted into the mid-gut, the differentiation of it commencing behind and proceeding forwards. In the Isopods, owing to the mesenteron not having a distinct cavity, the differentiation of it, which proceeds forwards as in Decapods, appears simply like a prolongation forwards of the proctodæum, the cells for the prolongation being probably supplied from the yolk. In Cymothoa the food-yolk is so bulky that a special yolk-sack is developed for its retention, which is not completely absorbed till some time after the alimentary canal has the form of a continuous tube. The walls of this yolk-sack are morphologically a specially developed part of the mesenteron.
Bibliography.
General Works.
(447) C. Spence Bate. “Report on the present state of our knowledge of the Crustacea.” Report of the British Association for 1878.
(448) C. Claus. Untersuchungen zur Erforschung der genealogischen Grundlage des Crustaceen-Systems. Wien, 1876.
(449) A. Dohrn. “Geschichte des Krebsstammes.” Jenaische Zeitschrift, Vol. VI. 1871.
(450) A. Gerstaecker. Bronn’s Thierreich, Bd. V. Arthropoda, 1866.
(451) Th. H. Huxley. The Anatomy of Invertebrated Animals. London, 1877.
(452) Fritz Müller. Für Darwin, 1864. Translation, Facts for Darwin. London, 1869.
Branchiopoda.
(453) Brauer. “Vorläufige Mittheilung über die Entwicklung u. Lebensweise des Lepidurus (Apus) productus.” Sitz. der Ak. d. Wiss. Wien, Vol. LXIX., 1874.
(454) C. Claus. “Zur Kenntniss d. Baues u. d. Entwicklung von Branchipus stagnalis u. Apus cancriformis.” Abh. d. könig. Gesell. der Wiss. Göttingen, Vol. XVIII. 1873.
(455) C. Grobben. “Zur Entwicklungsgeschichte d. Moina rectirostris.” Arbeit. a. d. zoologisch. Institute Wien, Vol. II., 1879.
(456) E. Grube. “Bemerkungen über die Phyllopoden nebst einer Uebersicht etc.” Archiv f. Naturgeschichte, Vol. XIX., 1853.
(457) N. Joly. “Histoire d’un petit Crustacé (Artemia salina, Leach) etc.” Annales d. Sciences Natur., 2nd ser., Vol. XIII., 1840.
(458) N. Joly. “Recherches zoologiques anatomiques et physiologiques sur l’Isaura cycladoides (=Estheria) nouveau genre, etc.” Annales d. Sciences Nat., 2nd ser., Vol. XVII., 1842.
(459) Lereboullet. “Observations sur la génération et le développement de la Limnadia de Hermann.” Annales d. Sciences Natur., 5th ser., Vol. V., 1866.
(460) F. Leydig. “Ueber Artemia salina u. Branchipus stagnalis.” Zeit. f. wiss. Zool., Vol. III., 1851.
(461) G. O. Sars. “Om en dimorph Udvikling samt Generationsvexel hos Leptodora.” Vidensk. Selskab. Forhand, 1873.
(462) G. Zaddach. De apodis cancreformis Schaeff. anatome et historia evolutionis. Dissertatio inauguralis zootomica. Bonnæ, 1841.
Nebaliadæ.
(463) C. Claus. “Ueber den Bau u. die systematische Stellung von Nebalia.” Zeit. f. wiss. Zool., Bd. XXII. 1872.
(464) E. Metschnikoff. Development of Nebalia (Russian), 1868.
(465) E. van Beneden. “Recherches sur l’Embryogénie des Crustacés. II. Développement des Mysis.” Bullet. de l’Académie roy. de Belgique, second series, Tom. XXVIII. 1869.
(466) C. Claus. “Ueber einige Schizopoden u. niedere Malakostraken.” Zeit. f. wiss. Zoologie, Bd. XIII., 1863.
(467) A. Dohrn. “Untersuchungen üb. Bau u. Entwicklung d. Arthropoden.” Zeit. f. wiss. Zool., Bd. XXI., 1871, p. 375. Peneus zoæa (larva of Euphausia).
(468) E. Metschnikoff. “Ueber ein Larvenstadium von Euphausia.” Zeit. für wiss. Zool., Bd. XIX., 1869.
(469) E. Metschnikoff. “Ueber den Naupliuszustand von Euphausia.” Zeit. für wiss. Zool., Bd. XXI., 1871.