INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY^ ETC. 791 



gordius it is almost certain that it is the very lowest of all known 

 Annelides ; the points in which it is lower affect chiefly the organiza- 

 tion of the nervous system, the characters of the ventral ciliary groove, 

 the blood- vascular system, and the relations of the midgut. 



These little worms (" Wurmchen ") are of yellowish- white colour, 

 and the sexually mature individuals are about 4 mm. in length ; they 

 creep about like Nemertines, and locomotion is principally effected by 

 cilia, while the direction they take appears to be influenced by the 

 longitudinal muscles of the body. Their general appearance is very 

 much that of Polygordius, the elongated body exhibits no external 

 segmentation, the ventral surface is rather flattened, and along the 

 trunk there is a deep ciliated groove. The cephalic portion, which is 

 somewhat thicker, has two flattened contractile tentacles at its anterior 

 end ; the hinder end is narrower and notched. Segmentation is ex- 

 pressed by the five boundary lines in the ectoderm, by the ciliation, as 

 well as by the dissepiments and the segmental organs. 



The cephalic region is distinguished by the possession of a very 

 large post-oral region, similar to that observed in Polygordius and 

 Saccocirrus. The number of trunk-segments increases during the 

 maturation of the generative products ; 22-31 segments were counted. 

 The last segments of all are always very small, and but imperfectly 

 differentiated in their histological details. 



As in the allied forms, the epidermis, the nervous system, and the 

 sensory organs stand in closer relations to one another than they do 

 in the more diflerentiated forms ; the epidermis is largely composed 

 of cubical cells, and a definite cuticle can hardly be made out ; between 

 these cells there are club-like mucous cells, opening to the exterior by 

 a fine orifice ; the cilia form, for the greater part, circlets, and of these 

 we find a double one in front of and a single one behind the mouth ; 

 while on the post-oral cephalic region there are foiu' circlets. On the 

 trunk-segments there is anteriorly and posteriorly another circlet, but 

 the cilia are delicate and sparsely distributed. The sensory hairs are 

 especially numerous on the tentacles, the anterior end, and on the 

 posterior segments, and there is also a better developed one on the 

 two terminal processes. 



The nervous system is difficult to make out in the living object, 

 the ganglionic nature of the frontal ganglion being indistinguishable, 

 and the presence of the organ merely indicated as a thickening of 

 the integument ; the sensory organs are represented by two transverse, 

 elongated, ciliated slits, placed on the dorsal surface of the anterior por- 

 tion of the head. There arc no pigmented eyes. Transverse sections 

 of specimens, suitably hardened and prepared, reveal a number of other 

 facts. The apparently sensory bodies connected with the frontal 

 plate are seen to consist -of a number of cells ranged round a central 

 point ; the inner part of the frontal ganglion is formed of a largish 

 mass of nerve-fibre; the neiglibouriug epithelium is considerably 

 thickened, but the cells are really all arranged in a single layer. Just 

 in front of the mouth the fibruus cord bifurcates to become connected 

 with the lateral i)arts of the ventral surface; in the post-oral cephalic 

 region they approximate towards one another. lu the first trunk- 



