ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 449 



arc also without this layer ; however, the question cannot yet be 

 regarded as settled with regard to the monogenetic forms of the latter 

 order. 



New Sense - organ in Mesostoma. * — The structure which 

 M. P. Hffllez regards as an olfactory organ in Mesostoma lingua, consists 

 of a small invagination on the ventral mid-line, between the mouth 

 and anterior extremity of the body. This small pit passes obliquely 

 forward, and ends in two lateral blind diverticula. The wall of the 

 pit is formed of cells similar to the epithelium of the ventral surface 

 of the body ; these are ciliated at the commencement of the pit, but 

 the author is uncertain how far inwards this condition is continued ; 

 here and there is a gland-cell. The sub-epidermic pigment surrounds 

 the pit, and streaks of it pass from this organ to the eye-spots. 

 Nerve-fibres from the ventral surface of the cerebral ganglia pass to 

 the ends of the diverticula. 



The author considers this structure sensory rather than glandular, 

 owing to the few gland-cells present; moreover, as Duges pointed 

 out, the quick perception of the presence of food by the Planarians 

 seems to indicate that some sense, other than sight due to their ill- 

 developed eyes, must be present. 



Mesostoma personatum.f — Dr. A. Jaworowski has a preliminary 

 notice of his studies on this Turbellarian. 



The cells of the epidermis are devoid of pigment, and in and 

 between them the rods are visible ; in some that have just escaped 

 from the egg the pharynx is not in the anterior or middle part of the 

 body, but behind, so that they appear to be species of 0_pisiovimn. 

 The orifice between the eyes and the pharynx is near the former in 

 young, while it is exactly between them in older forms. There is a 

 longitudinal and a circular layer of muscles, and the fibres anastomose 

 to form a plexus. The anterior part of the enteric cavity is pro- 

 portionately longer and larger in young than in adult forms; the 

 ventral portion of the parenchyma is much better developed than the 

 dorsal. The pharynx is a plexiform organ, which is made up of three 

 layers ; the outer and inner consist of longitudinal and circular 

 muscles, which anastomose with one another ; the median layer is the 

 best developed and consists of branching and plexiform fibres, in the 

 wide meshes of which the large cellular pharyngeal glands are to be 

 found ; there is a fourth, epithelial, layer. The water-vascular 

 system consists of two chief trunks, each of which divides into two 

 branches ; the anterior of these open in the epidermal invagination 

 between the eyes and the pharynx. The walls of the generative 

 organs consist of a close plexus, some uf the fibres of which are so 

 disposed as to have the appearance of being simple elements of 

 muscular fibres. 



Fresh-water MonotidEe.J— The discovery by Dr. Zacharias at 

 Hirschberg of a fresh-water Planarian belonging to Graaf's family 



♦ Comptes Kendus, cii. (1SS6) pp. 6S4-6. 



+ Zool. Anze.ig., ix. (188<d) pp. 83-5. 



X Bull. Soc. Vaud. Sci. Nat., xs.1 (1886) pp. 265~7'6 (I pi.). 



