Not only are the pleural ganglia fused to the cerebral, but also the visceral to these (see in further illustration the condition attained by the Pulmonate Limnaeus, fig.
The pond-snail (Limnaeus) furnishes, on the other hand, a very beautiful case of distinct ganglia and connecting cords (fig.
In Limnaeus the permanent shell is preceded in the embryo by a wellmarked shell-gland or primitive shell-sac (fig.
- Nervous System of the Pond knob - like particle Snail, Limnaeus stagnalis, as a type of the (Neritina and Palu- short-looped euthyneurous condition.
The nautiloid shell In Planorbis and in Auricula (Pulmonata, formed on the larva allied to Limnaeus) the olfactory organ is being cast, and a new on the left side and receives its nerve from shell of a different form the left visceral:ganglion.
The development of the aquatic Pulmonata from the egg offers considerable facilities for study, and that of Limnaeus has been elucidated by E.
The chief features in the development of Limnaeus are exhibited in fig.
- Embryo of Limnaeus stagnalis, at a stage when the Trochosphere is developing foot and shell-gland and becoming a Veliger, seen as a transparent object under slight pressure.
The outline of the velar area becomes strongly emarginated and can be traced through the more mature embr y os to the cephalic lobes or labial processes of the adult Limnaeus (fig.
- A, B, C. Three views of Limnaeus stagnalis, in order to show the persistence of the larval velar area v, as the circum-oral lobes of the adult.
The shell-gland is destined in Limnaeus to become very rapidly stretched out, and to disappear.
Such cannulated cells are characteristic of the nephridia of many worms, and the organs thus formed in the embryo Limnaeus are embryonic nephridia.
Limnaeus contains the largest species.
Physa is smaller than Limnaeus and has the upper part of the spire much shorter.
- Development of the Pond-Snail, Limnaeus stagnalis.