. Anatomischer Anzeiger. Anatomy, Comparative; Anatomy, Comparative. 312 The animal was Nais lacustris, a species in which the pro- stomium is greatly elongated forming a proboscis-like extension of the head. In this specimen there arises from the side of the prostomium a branch which is fully as long as the main prostomium, but a little more slender. The branch arises at a point some two thirds of the length of the main prostomium from the base and extends obliquely forward for some distance, then curving so that its tip lies directly in front of the tip of the main prostomium. Examination of
. Anatomischer Anzeiger. Anatomy, Comparative; Anatomy, Comparative. 312 The animal was Nais lacustris, a species in which the pro- stomium is greatly elongated forming a proboscis-like extension of the head. In this specimen there arises from the side of the prostomium a branch which is fully as long as the main prostomium, but a little more slender. The branch arises at a point some two thirds of the length of the main prostomium from the base and extends obliquely forward for some distance, then curving so that its tip lies directly in front of the tip of the main prostomium. Examination of the mounted specimen shows that the structure of the branch is in all respects similar to that of the main trunk. Unfortunately no observations were made upon the living animal concerning the position and use of the organ. It appears probable that this anomaly has arisen in consequence of some injury to the prostomium which has resulted in new growth at a point along the side. The kind of injury required to produce the result can be determined only by experimentation. It is possible that an injury upon one side of the prostomium might give rise to a growth of this kind. In consequence of such an injury regeneration pro- ceeding from the posterior side of the wound might lead to the formation of a branch like that figured. The inequality of the two branches would appear to indicate that they were not formed in consequence of the loss of the prostomium-tip. One point is of special interest: the branch is about as long as the main prostomium, i. e. a new prostomium of full lenght has arisen from a point near the tip of the original prostomium, just as it would arise if the latter were cut off at its base. If this be the result of regenerative processes, the lateral region of the prostomium, as well as its base, is capable under certain conditions of giving rise to a prostomium of full lenght. Hull Zoological Laboratory, university of Chicago, February Please note that thes
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