Ohservations on the Orihatidse. By A. D. Michael. 21 



colourless sac, may be seen on eacli side of the body, the seemingly 

 blind end being nearest to the eye ; the sac descending obHquely 

 downward and slightly forward, and being attached close to the 

 acetabulum of the coxa of the second leg; a closer examination 

 shows that this is not the only attachment, but that the lower end 

 is apparently bifurcated, and that the second branch is attached 

 much nearer to the centre of the body, and higher in level than 

 the coxal branch. On dissecting out this sac, and carefully ex- 

 tending it, a matter by no means easy, it will be found that what 

 seemed to be the blind end was not the end at all, but that the 

 whole organ is an elongated, sausage-shaped sac, bent upon itself in 

 the middle and taking a single turn, so that the two halves cross, 

 but for some distance the two limbs of the horseshoe (if I may call 

 them so) lie over each other, or are so closely pressed against one 

 another as to appear one; it is only toward the ends that they 

 stand free from each other when in situ. The general position of 

 the organ in the body is shown at plate I. fig. 8 ; acd the organ 

 unfolded and showing so much of its minuter structure as I am 

 acquainted with at plate I. fig. 9. The walls of the sac are colour- 

 less but highly granular, and apparently of considerable thickness, 

 and, it appears to me, decidedly glandular. Within the sac, i. e. 

 either on its inside surface or in the substance of the wall, and near 

 to the centre (long axis) of the sac, is a double row of highly re- 

 fractive points, arranged at regular distances, those of the two rows 

 not being opposite, but alternate. A fine distinct double line may 

 be seen uniting these alternate points so as to form a double zig- 

 zag line all along the organ, the refracting points being slight 

 prolongations of the zigzags. Three possible explanations of this 

 structure would seem to ofier themselves. 1. That the double lines 

 are tubules as in the nephridia of Yermes. 2. That the space 

 between the fine lines is really the zigzag lumen of the sac, 

 possibly running between cells projecting alternately from the 

 opposite walls, and having a cuticularization at the refractive 

 points. 8. That the whole (zigzag and points) is a cuticular 

 strengthening on the interior wall of the sac, the cuticularization 

 being greatest at the refractive points which may be intercellular. 



Connected with this tube is a globular body, which has thick 

 but less granular walls, and which is probably hollow; both the 

 gland and this body, when pressed, discharge liquid. There is 

 not any sign of air in either. 



What is the ofiice of this organ ? I cannot, of course, pretend 

 to do much more than guess, but if a suggestion be allowable, I 

 would point to the nephridia (segmental organs) in Yermes, and 

 the green gland in Astacus and otber crustacea, and the coxal 

 glands in Scorpio and Limulus, as those where the analogy may 

 be sought. The resemblance to the former, in particular, is very 



