Fig. 20a, b, c, d, e. Five sections through an embryo of the same age as fig. 9. a and b are sections through the procephalic lobes, c through the front part of the thorax. d cuts transversely the posterior parts of the thorax, and longitudinally and horizontally the ventral surface of the abdomen. e cuts the posterior part of the abdomen longitudinally and horizontally, and shews the commencement of the mesenteron.
Fig. 21. Longitudinal and vertical section of an embryo of the same age. The section passes somewhat to one side of the middle line, and shews the structure of the nervous system.
Fig. 22. Transverse section through the dorsal part of the abdomen of an embryo of the same stage as fig. 9.
[471] From the Quarterly Journ. of Microscopical Science, Vol. XX. 1880.
[472] I was unfortunately too much engaged, at the time when the eggs were collected, to study them in the fresh condition; a fact which has added not a little to my difficulties in elucidating the obscure points in the early stages.
[473] “Beiträge z. Entwick. d. Lepidopteren,” Jenaische Zeit., Vol. XI. p. 124.
[474] If Grobben's account of the development of Moina is correct this statement must be considered not to be universally true.
XVIII. On the Spinal Nerves of Amphioxus[475].
In an interesting memoir devoted to the elucidation of a series of points in the anatomy and development of the Vertebrata, Schneider[476] has described what he believes to be motor nerves in Amphioxus, which spring from the anterior side of the spinal cord. According to Schneider these nerves have been overlooked by all previous observers except Stieda.