The rostral nervous system of a 6.7 mm red-necked wallaby Notamacropus rufogriseus embryo (MS399)

Introduction

Notamacropus rufogriseus is the red-necked wallaby or Bennett’s wallaby, found naturally in coastal eastern Australia from Queensland to Tasmania, but with many introduced populations now found throughout NZ, the UK and Europe.

Methods

The specimen is part of the Hill collection stored at the Museum für Naturkunde in Berlin.  MS399 is listed as Macropus rufficollis (sic) an embryo of 6.7 mm greatest length (GL) with 35 to 36 somites, slides 1 to 12, sectioned at 10 µm in a transverse plane.  The stain appears to be hematoxylin and eosin.  Macropus rufficollisis now designated Notamacropus rufogriseus.  The embryo was probably collected in the early 20th century in eastern New South Wales.

Description

The specimen shows an embryo with a closed neural tube and clear division of the rhombencephalon and diencephalon into rhombomeres and prosomeres, respectively. The cerebellum (Cb in Plates 3, 4) is rudimentary and elaboration of the otocyst (Oto in Plates 2 to 4) is confined to the elongation of an endolymphatic diverticulum (ELD in Plates 2, 3).  The trigeminal ganglion (5Gn in Plates 5 to 7) is large and lies alongside rhombomere 2 (r2 in Plates 4 to 6).  The facioacoustic ganglion complex (fag in Plates 4, 5) is differentiating into distinct geniculate (facial), vestibular and cochlear ganglia.  The forebrain is rudimentary and its most distinctive feature is the optic vesicle (opt in Plates 9, 10) with early sensory (neural) retina (retina in Plates 9, 10) and future pigment epithelium (pig in Plates 9, 10).  The origin of the optic cup is aligned with the acroterminal part of the hypothalamus (hyat in Plates 8 to 10).  An optic placode (optpl in Plates 9, 10), for the developing lens, overlies the optic cup.