436 



Bashford Dean Memorial Volume 



TABLE III. 



Length of the mesonephros in proportion to the total body length and to the entire length of the body- 

 cavity, in four female specimens of Chlamydoselachus, shown in percentages. The specimens are arranged 

 in the order of sexual maturity. 



Specimen Number 



IV. 



in. 



I. 



II. 



Length of Mesonephros 

 Total Body Length 

 Length of Mesonephros 

 Length of Body Cavity 



34.7 

 87.7 



35.7 

 87.3 



38.3 

 88.0 



40.7 

 88.1* 



*Percentage computed from the right mesonephros only. 



icant of either developmental or retrogressive changes. Therefore I conclude that there 

 is no appreciable change in the length of the mesonephros proportional to body length 

 or to the length of the body cavity, within the age limits represented by my specimens. 

 From dissections, one gets the impression that the mesonephroi originally extended 

 a Httle further forward, since vestiges of these organs appear in front of the unequivocal 

 portions represented in the figures. In any event, the length of the mesonephros in the 

 female Chlamydoselachus is remarkable. In many of the more highly differentiated 

 elasmobranchs (e.g., the skates) only the posterior portion of the female mesonephros 

 persists in the adult. In Chlamydoselachus, the presence of the mesonephros through- 

 out almost the entire length of the body cavity of the female must be accounted a 

 primitive character. 



Throughout their entire extent, the mesonephroi lie against the dorsal body wall, 

 close to the median Hne. At their posterior ends they are actually united, but they 

 diverge a Httle anteriorly. Therefore, along the greater part of their course they He 

 along the low ridge formed by the vertebral column, but at their anterior ends they 

 depart sHghtly from this ridge. In specimens TV, III and I, the mesonephroi He almost 

 flat against the dorsal body wall; therefore in Text 'figures 85, 86 and 87, which are drawn 

 from these specimens, the mesonephroi are shown very nearly in broad view. Variations 

 in the width of the mesonephroi are fairly well shown in these figures. In specimen No. 

 Ill, which has the largest mesonephroi, each mesonephros has a maximum width of 13 mm. 

 In specimen No. II (Text-figure 88), within the posterior half of the body cavity the 

 mesonephroi are approximated to such a degree that the surfaces ordinarily dorsal are 

 medial. Hence, in a ventral view, the mesonephroi are seen almost on edge, so that 

 their actual width is not fully represented in the figure. In the anterior half of the body 

 cavity of No. II, the mesonephroi gradually become flattened against the body wall as 

 they diverge anteriorly. 



There is considerable variation in the extent of union of the mesonephroi at their 

 posterior ends. In specimen No. IV the two mesonephroi are united across the median 

 plane for a distance of about 80 mm. measured from their posterior ends; in No. Ill, 



