26 ILLINOIS BIOLOGICAL MONOGRAPHS [314 



114/j to Linstow. Calcareous bodies in the characteristically fine parenchyma, 

 described by Moniez and Zernecke, and given dimensions of 13 by 7.8)u by 

 Linstow, were observed in the largest living specimens from the body-cavity 

 of Catostomus commersonii commersonii to be extremely numerous, spherical to 

 ellipsoidal in shape and to measure from 14 to 19/i in length by 12 to 17 in 

 breadth. 



The musculature has been well described histologically by Zernecke (1895); 

 while KiessUng spoke rather briefly of its arrangement in the late larva. Later 

 Llihe dealt with the system in general (1897a and 1898) and its relation to the 

 nervous system (1896), and Linstow (1901a), gave a concise account of its 

 arrangement. 



The chief nerve strands are situated in transections between the lateral 

 and median quarters of the transverse diameter of the strobila, in the median 

 frontal plane, that is below the neighboring testes, and with a diameter of 50 

 to lOO^u. The details of the system have been studied by Moniez (1881), 

 Niemiec (1888), Zernecke (1895), and Cohn (1898), the latter of whom found 

 conditions pretty much as in Schistocephalus, namely, that each chief strand 

 has associated with it six collateral strands, arranged in three groups of two 

 each. 



The excretory system was studied by Moniez and Zernecke in considerable 

 detail. Linstow stated that two regions accommodating numerous longi- 

 tudinal vessels are present: (1) an outer, close beneath the vitelline glands, 

 and (2) an inner, between the inner longitudinal and transverse muscles, or as 

 Linstow figured, between the former themselves. In the material studied an 

 outer plexus appeared close beneath, among, or most often just outside of the 

 vitelline glands (cortical); a second and quite indistinct one among both sets 

 of muscles, and a third, or innermost layer, as prominent as the outermost, 

 almost in the median frontal plane of the medulla. 



The sets of genitalia, beginning about 10mm. from the anterior end and 

 very closely crowded together in the longitudinal direction, lie from 0.05 to 

 0.20mm. apart, 0.13 to 0.15mm. being the data given by Linstow. The open- 

 ings are usually almost exactly in a transverse line; but the cirrus and uterus 

 openings alternate irregularly from side to side, that of the vagina being con- 

 stantly in the middle. This alternation of the openings is due to the similar 

 alternation of the internal organs and evidently was the basis upon which the 

 earlier species L. digramnia and L. alternans were established. The genital cloaca 

 is a quite irregular transverse depression, 0.18 to 0.20mm. in width and 0.02 

 to 0.03mm. in length, the respective measurements by Linstow being 0.106 

 and 0.026mm. 



"The testes lie in a single row, which is only interrupted by the uterus, on 

 the dorsal side of the medulla. ..." They are from 20 to 40 in number in 

 transections, ellipsoidal in shape, their greatest diameters being transverse, as 

 indicated by the maximum width, length, and depth being, respectively, 115 to 

 145, 45 to 55, and 80 to 85^. Linstow gave them as 150 to 180/x long by 88 to 

 156ju wide. The loosely coiled vas deferens is situated above the cirrus-sac 



