308 Br. L. Bohmig on the 



XL. — On the Sense-organs of the Turhellaria. 

 By Dr. L. Bohmig *. 



Being engaged in investigations upon the Dendrocoelous and 

 Ehabdocoelous Turbellaria, I wisli here to communicate what 

 I have at present ascertained witli regard to their sense- 

 organs, as the publication of ray larger memoirs relating to 

 the general structure must be delayed for some time in conse- 

 quence of the accumulation of material and the preparation of 

 figures. 



A comparison of my preparations of Planaria gonocephala, 

 Duj., with the figures and descriptions which J. Carrifere has 

 given t of the eyes of Planaria polychroa and Dendrocoelum 

 lacteum has convinced me that I am able to furnish some 

 fresh details. 



The position of the eyes in Planaria gonocephala is the 

 same as in all the Triclades known to me, namely in the 

 anterior extremity of the body, described as the head. Pla- 

 naria gonocephala has a triangular head, and the eyes lie in 

 its middle. The longitudinal diameter of the eyes amounts 

 to about 0"18 millim., that of the width and height about 0*1 

 millim. Sections through the eye allow us to recognize what 

 follows. 



Each eye consists of a pigment-capsule and a nervous 

 apparatus ; the pigment-capsule, the greater diameter of 

 which is parallel to the longitudinal axis of the animal, 

 consists of small blackish-brown spherules. The convex 

 side of the capsule is surrounded by a narrow border of finely 

 granular plasma, in which a number of distinct round nuclei 

 are to be perceived. The great number of nuclei indicates 

 that the pigment-capsule has originated from several cells, in 

 opposition to the eyes of the Polyclades, in which only one 

 nucleus occurs in this plasmatic border. 



Before the opening of the pigment-capsule is the so-called 

 ganglion opticum^ which consists of a central ball of dotted 

 substance, around which peripheral ganglion-cells (retinal 

 cells) are grouped. The central nervous system is in con- 

 nexion with the ball of dotted substance through the nervus 

 oj^ticus. This originates from a part of the cerebrum where 

 the dotted substance is characterized by greater fineness and 

 a more homogeneous appearance. The same thing occurs in 



* Translated from the ' Zoologischer Anzeiger,' no. 260, 12th Septem- 

 ber, 1887, pp. 484-488. 



t J. Carriere, "Die Augen von Planaria polT/chroa, 0. Schm., und 

 Polycelis nigra, Ehrb.," in Arcliiv fiirmicrosc. Anat. Bd. xx. Heft 2 ; and 

 " liie Sehors-aue der Thieve.'' 



