Journal of Morphology

The diversity of the mammalian allantois is known to be different in size and form. Here, we show, in addition, (1) specific characteristics of the endodermal component accompanied by mesoderm and early blood vessels (bv) and surrounded by mesothelium with diversified cell contacts and microvilli, (2) interspecific differences in Brachyury expression, and (3) specific presence and absence of cells resembling primordial germ cells (pgc). We propose a hitherto unsuspected variation (a) in allantoic function prior to placenta formation, and (b) in mechanisms of the allantoic development through tissue interactions.

Dynamic osteogenesis in Pogona. A layer of flattened mesenchymal cells form the periosteum. Preosteoblasts and osteoblasts are all polarized in the same direction: the nucleus and the endoplasmic reticulum are aligned in an axis parallel to the front of the secreted unmineralized bone matrix. Osteoblasts move back as they secrete collagen fibers, forming a migrating lamina of cells.

The major morphological changes in key internal structures during blow fly metamorphosis are documented with micro-CT. A quantitative analysis of the development of selected organ systems is provided for the first time in cyclorrhaphous dipterans

Post-metamorphic development of skin glands in a true toad. Skin glands in juveniles smaller than 50 mm have an immature morphology. Toxic parotoids grow allometrically but dorsal skin glands grow isometrically.

In watersnakes (Nerodia), the placenta formed from the chorioallantois + uterus shows specializations for gas exchange. The yolk sac placenta lacks such specializations and becomes replaced during development by the chorioallantoic placenta as fetal needs for gas exchange increase.

Dense capillary beds are one of several specializations for maternal-fetal gas exchange in the chorioallantoic placenta of watersnakes. In late development, the yolk sac placenta shows cellular specializations for yolk digestion and evidence of maternal-fetal nutrient transport.

The schematic diagram demonstrates the spermiogenesis of Penaeus monodon. From a stage I spermatid (StI) to a stage III spermatid (StIII), some mitochondrion-like bodies (MLB) expand into multi-layered lamellae and later the lamellae convert to pre-acrosomal vesicles (PV) and endoplasmic reticula (ER). Numerous PVs merge together to form an acrosomal chamber (AC) and within the AC a dense anterior acrosomal body (AB) begins to be assembled. From a stage IV spermatid (StIV) to a stage V spermatid (StV), the AC grows larger and the AB becomes denser, a dense plate (DP) forms at the junction of AB and plasma membrane. From a StI to a StV, the nucleus (N) gradually transforms from a condensed state to a decondensed state. From a StV to a StVI, the nuclear envelope degenerates, the nucleus is filled with diffused chromatin, and the AB occupies the majority of AC. Most spermatozoa in the testis (TSz) contain a highly decondensed nuclei and a subacrosomal chamber (SbAC) emerges between the nucleus and AC, while the growth of spiky acrosome and modification of chromatin are finally completed for spermatozoa in the spermatophore (SSz).

Orientation of the lateral semicircular canal of the inner ear within the skull of extant xenarthrans (Mammalia). Upper skull: in the extant armadillo Dasypus kappleri. Lower skull: in the extant three-toed sloth Bradypus tridactylus. The red lines mark the plane of the lateral semicircular canal, which is more oblique in armadillos than in sloths (relative to the palate).

afln, abfronto-lateral nerve; am, abfrontal muscle; an, abfrontal nerve; fm, frontal muscle; fn, frontal nerve; lfn, latero-frontal nerve; pc, peritoneal cell.