OF OECANTHUS AND TELEAS. 271 



that the protoplasmic fluids of the body cavity can pass freely into the lumen of this 

 appendage. The salivary glands were not detected in any of the liviug parasites, but on 

 transverse sections of this stage they are found in various degrees of development. They 

 arise as solid rods of mesodermic elements in which a small but gradually increasing lumen 

 early makes its appearance. (PI. 25, fig. 17.) These rods are derived from the lateral 

 edges of the ventral stripe, and lie one on each side of the incompletely developed nervous 

 cord, which at this time they approximate in size. 



At the beginning of this stage the ventral stripe was seen in its primitive state as a 

 layer of enlarged hypodermal cells along the median ventral line. These cells, together 

 with the mesodermic elements, soon form by a rapid proliferation a thick, ventral cell plate 

 or bed. The derivatives of the hypodermal cells are from this time on to be distinguished 

 from the mesodermic elements. The hypodermal cord is more and more differentiated, 

 until it becomes sharply defined from the surrounding mesoderm. It exhibits an enlarge- 

 ment at each end, and at one-third of the distance from the cephalic end a less conspicuous 

 swelling, while between this latter and the head end it forms a ring around the oesophagus. 

 The cephalic termination is the primitive brain mass. (PI. 25, figs. 9, 19 ; pi. 24, figs. 23, 

 25.) The abdominal enlargement consists of the last abdominal ganglion and the sexual 

 cells, and is in close connection with the proctodaeum. The middle enlargement is the 

 suboesophageal ganglion and lies in the depression formed by the folds of the lower lip, 

 only a short distance behind the oesophageal ring. The brain mass consists of a cortical 

 layer of spindle-shaped cells with their long axes arranged in a manner radial to the centre 

 of the mass. The central portion of the brain region in pi. 24, fig. 23, represents a surface 

 view of these elongated cells, which consequently appear round. The central mass is com- 

 posed of small, irregularly disposed, and frequently ill-defined cells. The brain varies 

 much in shape even in individuals of the same degree of development ; it may be oval or 

 quadrangular on side view, and its dorso-ventral axis is usually greater than its longitudi- 

 nal. It is continuous on its ventral face with the nervous cord, which divides soon after 

 leaving the brain to form the oesophageal commissure. The commissural cords unite soon 

 after passing the oesophagus and enlarge into the suboesophageal ganglion. (PL 24, figs. 

 23,25; pi. 25, figs. 18, 19.) The latter is circular in transverse section, long oval in 

 longitudinal section. It lies between the cup-shaped cuticular structures, and in the cavity 

 formed between the folds of the lip. From this ganglion the cord extends along the 

 curved outline of the ventral wall of the body and enlarges into a pyriform mass which 

 near its middle point is curved upwards around the end of the mesenteron. From the up- 

 curved end of this fold the germs of the sexual organs are budded off as a varying number 

 of cells (2 — 6) imbedded in a homogeneous protoplasm. They appear in sections of hard- 

 ened specimens as though formed endogenously within the substance of the still persisting 

 mother cells. (PI. 25, fig. 11.) In pi. 25, fig. 13, is shown a section of one of the primi- 

 tive sexual masses. The section passes through three cells of similar size. One of these 

 shows within its cell wall two spherical cells, within which is contained all the proto- 

 plasm of the mother cell. These derivative cells have definite cell walls and a distinct 

 nucleus, indicating their origin by endogeneous cell formation. The different shapes of the 

 sexual germs are seen by comparing pi. 24, figs. 21, 23, 25, 26, 30, and pi. 25, figs. 1-5, 

 11, 13, 16, 18. During this stage they become entirely separated from the ner- 



