A Description of three Acoela from the Gulf of Naples. 
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food {fd). The parenchyma of Monochoerus illardatus contains zoochlo- 
rella cells, but that of Monochoerus lineatus does not. In other respects 
the two tissue agree in structure and arrangement. 
The structure of the nervous system has not been studied. In the 
anterior end a large statocyst is surrounded by nerve cells and on each side 
of the statocyst at the same level with it are the red eyes (pi. 10, fig. 6, e), 
Monochoerus linaeatus, hke other Acoela, is hermaphrodite, the male 
and female sexual organs occurring in the same individuai, the former 
ripening before the latter. Paired testes he on each side of the body, 
and extend far forward, almost reaching the level of the statocyst. In 
the testes which are follicular in structure, the developing spermatozoa 
can be seen. 
The large penis is enclosed in a sheath (fig. 8, ps) surrounded by 
glandulär tissue. On each side of the penis are two rudimentary canals 
(aa and ap) which no doubt correspond to the "Adenodactylus anterior" 
and "posterior" of Monochoerus illardatus. The penis is evertible, and 
at the time of copulation it is extruded from the genital opening. Two 
copulating individuals were found and were kiUed in order to study from 
sections, the relation of the copulating organs. Unfortunately during 
the process of imbedding, the animals were broken apart, and the struc- 
tures were so much injured that it was impossible to determine the rela- 
tion of the parts. When the worms copulate they unite by their ventral 
surfaces (fig. 6), so that the posterior ends overlap, while the anterior 
ends extend in opposite directions. 
Careful investigation of serial sections, both transverse and sagittal, 
has failed to reveal the presence of a female genital orifice in front of 
the male opening. There seems to be no direct communication between 
the bursa seminahs and the exterior. Löhner and Micoletzky (1912) 
have found in Monochoerus illardatus, that a cihated tube, the vagina, 
leads from the antrum femininum, and enters the posterior side of the 
bursa seminali s. No such canal has been found in Monochoerus lineatus. 
Here there is a canal leading from the male genital opening, first in a 
dorsal direction then toward the anterior, and finally entering a cavity 
which may be a "Penisblase" such as has been demonstrated in Mono- 
choerus illardatus, but which appears to lead directly into the bursa 
(fig. 8, gd). As no other communication between the bursa and the 
exterior has been found I am inclined to think that the spermatozoa 
from another worm enter the bursa in this way. If this be true then 
the opening to the exterior (go) should be called the atriumi genitale 
commune. 
