i6 



THE TURBELLARIA 



As sense organs, the Turbellaria present eyes which are simple, 

 epidermic, pigment spots in Acoela, and in a few other cases, but 

 they usually sink below the epidermis and lie in the parenchyma ; 



8 



i' 



FIG. V. Anatomy of the Acoela. 



1. The nervous system (modified after Bohmig). a, brain ; b, marginal (lateral) nerve ; 

 c, dorso-lateral nerve ; d, dorsal nerve ; e, ventral nerve. The nervous network of the dorsal 

 surface is represented on the left ; that of the ventral surface on the right, where the dorso- 

 lateral nerve (c') is cut short. /, otocyst ; g, ventral nerve commissure connecting the two 

 ganglionic masses () of the brain. 



2. Longitudinal section through the anterior end of the body, a, brain ; g, ventral com- 

 missure ; /, otocyst ; h, frontal gland. 



3 and 4. Chlorophyll bodies of Convolute (after Haberlandt). a, protoplasm of the cell ; 

 iloropl 

 mgh a 

 of the cell are starch granules ; b, the nucleus. 



6, its nucleus ; c, chloroplast or envelope of chlorophyll ; d, pyrenoid. 



5. Section through a chlorophyll body (after Haberlaudt). The black dots in the centre 



6. Otocyst. a, the wall formed of two cells ; Z>, one of the two nuclei ; c, the otolith cell 

 with its nucleus. 



7. Half a transverse section across Convoluta in the region of the mouth (after v. Graff). 

 a, epidermis ; b, muscular coat, consisting of outer circular, and inner longitudinal fibres ; 

 c, gland cells opening on to the surface ; d, peripheral parenchymal cells ; e, nucleus of deeper 

 parenchyma cells ; /, lacunae in the parenchyma ; g, dorso- ventral muscles with their nuclei ; 

 h, ovum, in the ovary, which is not marked off in any way from the surrounding parenchyma ; 

 . i, mouth opening directly into the central mass of parenchyma ; fc, ventral nerve tract ; I, 

 marginal nerve ; m, dorso-lateral nerve ; n, dorsal nerve. The chlorophyll bodies are omitted. 



8. Half of a transverse section of Haplodiseus (after Bohmig), to show the differentiation 

 of the parenchymal tissue into (d) peripheral syncytium, with round nuclei forming a layer 

 underlying the muscular coat ; e, intermediate or general mass of amoeboid and star-shaped 

 cells ; and fc, a digesting, central syncytium ; other letters as in 7. 



they then have a definite and peculiar structure. An otocyst, 

 discovered in Monocelis by Erey and Leuckart, occurs in the 

 Acoela (Fig. V. 6), the Monotidae, and Mecynostoma. Ciliated pits 



