cyclostoma

The tenth stage is formed by those low fishes in which the spinal rod is differentiated into the skull -- and the vertebral-column, called the single-nostriled animals (monorrhini), and represented by the cyclostoma of today (hag and lampreys).

The Theories of Darwin and Their Relation to Philosophy, Religion, and Morality Rudolf Schmid

In these "telolecithal" ova, or ova with the yelk at one end (for instance, in the cyclostoma and amphibia), the gastrulation then usually takes place in such a way that in the cleavage of the impregnated ovum the animal (usually the upper) half splits up more quickly than the vegetal (lower).

The Evolution of Man — Volume 1 Ernst Heinrich Philipp August Haeckel 1876

Unequal segmentation takes place in some of the cyclostoma and in the oldest fishes in just the same way as in most of the amphibia.

The Evolution of Man — Volume 1 Ernst Heinrich Philipp August Haeckel 1876

In most of the members of this stem the two are united in a single urogenital system; it is only in a few groups that the urinary and sexual organs are separated (in the amphioxus, the cyclostoma, and some sections of the fish-class).

The Evolution of Man — Volume 1 Ernst Heinrich Philipp August Haeckel 1876

The oldest sharks (Cestracion) still have the unequal segmentation inherited from the cyclostoma.

The Evolution of Man — Volume 1 Ernst Heinrich Philipp August Haeckel 1876

Unequal total segmentation follows the same lines in the oldest fishes, the selachii and ganoids, which are directly descended from the cyclostoma.

The Evolution of Man — Volume 1 Ernst Heinrich Philipp August Haeckel 1876

Although this unequal segmentation of the cyclostoma, ganoids, and amphibia seems at first sight to differ from the original equal segmentation (for instance, in the monoxenia, Figure 1.29), they both have this in common, that the cleavage process throughout affects the

The Evolution of Man — Volume 1 Ernst Heinrich Philipp August Haeckel 1876

The gastrulation of the primitive fishes or selachii (sharks and rays) has been carefully studied of late years by Ruckert, Rabl, and H.E. Ziegler in particular, and is very important in the sense that this group is the oldest among living fishes, and their gastrulation can be derived directly from that of the cyclostoma by the accumulation of a large quantity of food-yelk.

The Evolution of Man — Volume 1 Ernst Heinrich Philipp August Haeckel 1876

Among the cyclostoma ( "round-mouthed") the familiar lampreys are particularly interesting.

The Evolution of Man — Volume 1 Ernst Heinrich Philipp August Haeckel 1876

In respect of organisation and development they are half-way between the acrania (lancelet) and the lowest real fishes (Selachii); hence I divided the group of the cyclostoma in 1886 from the real fishes with which they were formerly associated, and formed of them a special class of vertebrates.

The Evolution of Man — Volume 1 Ernst Heinrich Philipp August Haeckel 1876