PROTEOCEPHALUS AMBLOPLITIS LEIDY 189 



SESSIONAL PAPER No. 39b 



specimen of the former condition which shows signs of segmentation being only 

 39 mm. long. In this specimen (PI. XIX, Fig. 6) the apex of the scolex is very 

 prominent and is occupied almost wholly by the end-organ which is somewhat 

 flattenBd dorso-ventrally as is the scolex itself and. measures 426 by 360^ in the 

 cross-section by 380;i in length. Furthermore, the basal cells are represented by 

 only small remains with here and there short processes, and widely-separated radi- 

 ating pieces represent the strands connecting them with the central tube of the 

 organ. The aperture is relatively quite large. The contents show larger granules, 

 while only that part at the posterior end of the tube seems to be very fluid. When 

 fresh material is fixed it is a common occurrence to see a short, thick, viscid stream 

 of liquid oozing from the apex of the scolex. As soon as this material comes in 

 contact with the fixing-fluid, it coagulates, thus demonstrating its protein nature. 

 Microchemical tests show that it contains lime-salts, while the basal cells are like- 

 wise rich in calcium. From this it would appear that the basal cells secrete the 

 material found in the cavity of the organ, but whether the material is for digestion 

 in connection with the boring action which some authors attribute to the plerocer- 

 coids, for adhesion or merely represents the remains of a much-altered rostellum, 

 perhaps in connection with excretion, must remain conjectural until further study 

 throws more light on the subject. 



The study of plerocercoids intermediate in length between that just described 

 and the 39 mm. specimen mentioned above, showed that besides the general growth 

 and differentation of all of the tissues there is particular development in the cuti- 

 cula, end-organ and excretory vessels. 



The cuticula as a whole gets much thicker while its external layer becomes 

 relatively thinner. The end-organ grows comparatively rapidly until it occupies 

 almost the whole of the apex of the plerocercoid (Plate XIX, Fig. 6). Its de- 

 generation into the calcareous bodies of the adult scolex must take place very 

 quickly, as has been demonstrated for P. filaroides by LaRue. Unfortunately I 

 have not yet procured specimens showing this degeneration. 



In the 39 mm. plerocercoid the excretory vessels are three or four on each 

 side in the neck region. One pair lying in a " median frontal plane" (Benedict) 

 are the largest and most regular of them all ; few branches are given off from them 

 in the scolex where they gradually diminish in size and disappear near the apex. 

 Another pair giving off many branches, a large number of which go to the exterior, 

 lies in a sagittal plane on each side of the body just outside the first vessel but 

 within the longitudinal body-muscles, thus forming the base of a triangle whose 

 apex is the largest vessel. Other large vessels in the region of the scolex are 

 merely branches, but some run parallel to the main vessels for considerable dis- 

 tances, and one may develop into a fourth vessel. This latter statement refers 

 especially to one seen outside the longitudinal muscle zone, about half-way between 

 it and the cuticula. This arrangement ot vessels is also found in specimens only 

 10 mm. long, where even a fifth vessel may be seen running parallel to the others 

 for a short distance. However, when these vessels are traced backward, they all, 

 excepting the smaller pair in the median frontal pair unite to foim the single pair 

 of large vessels, evidently ventral in position, which course irregularly backwards 



