The Anatomy of Chlamydoselachus 443 



Transverse serial sections of the excretory system of specimen No. I were taken from 

 a region near the center of the body cavity, where the mesonephric ducts course in the 

 oviducal mesenteries; also from a region just posterior to the shell glands, where the ducts 

 run in the dorsal mesentery. In each case the right duct is decidedly smaller than the 

 left. In these sections of the mesenteries, the collecting tubules have much thicker walls 

 than the arteries and veins; so it is unlikely that, in dissections, any blood vessels were 

 mistaken for collecting tubules. 



In specimen No. II, due to poor preservation and excessive mutilation of the mesen' 

 teries, only fragmentary portions of the mesonephric ducts and collecting tubules could 

 be found. In their si2;e and distribution these portions conform to the general plan revealed 

 in my other specimens, particularly in No. I. 



mes. (L. 



oud.mes. 



ct. r.m,. 



Text-figure 93. 



Excretory organs of the right side of a female C\i\avivjA.osdac\vxi in right lateral view, one-fourth 



natural size. The broken line, indicates the junction of the dorsal mesentery with the oviducal 



mesenteries. The ventral region is uppermost. 



ex., collecting tubule; mes.d., mesonephric duct; ovd.mes., line of attachment of the right oviducal mesentery to the 



right oviduct; r.m., right mesonephros; r.u.s., right urinary sinus. 



Drawn from specimen No. I in the American Museum of Natural History. 



The posterior portions of the mesonephric ducts of Carman's specimen (1885.2) 

 are illustrated in my Text'figure 92. In this figure, as already noted in my account of the 

 urinary sinuses, the mesonephric ducts are shown uniting to form a single large duct 

 posteriorly. Hawkes (1907) states that in the female C\Aa'my&os,dac}\us: "The same 

 mesentery which supports the oviduct also supports the urinary sinus and the mesone- 

 phric ducts. The latter pass from the kidney at regular distances, there being approxi- 

 mately one to each myotome." This description of the mesonephric ducts is doubtless 

 intended for the collecting tubules. 



In the account of the urethral apertures and urinary sinuses of my four specimens, 

 I have noted occasional deficiencies in these features on the right side. It remains to call 

 attention to some observed instances of deficiency in the duct system on the right side. 

 In specimen No. I the mesonephric ducts and collecting tubules, though well developed 

 on both sides, are slightly smaller on the right. In specimen No. Ill the right mesonephric 

 duct is of microscopic si2;e, though the left duct is well developed for at least 50 mm. 

 in front of the urinary sinus. We might attribute these defects to pressure from the 

 right uterus, which is enormously enlarged while the young are being carried, were it 

 not for the fact that the most extensive defects occur in No. Ill, which is evidently not 

 quite mature. It seems more likely that the tendency to shift the burden of excretion on 

 to the left side is due to germinal variations which, however, are adaptive in view of the 

 unbalanced development of the reproductive organs of the right side. 



