4 Transactions of the Society. 



shown in fig. 7, which is a female ; but it must be remembered that 

 no two specimens agree exactly in the relative size, shape, and 

 arrangement of the various organs ; indeed the two sides rarely 

 absolutely correspond. Moreover, in consequence of the highly elastic 

 and extensile nature of some of the parts, considerable differences 

 occur in the appearance of the same side of the identical specimen 

 from time to time ; the general arrangement is, however, naturally 

 always similar. The mouth-opening in Uropoda is in the ventral 

 plate, some little distance from the point of the rostrum, and conse- 

 quently the alimentary canal does not commence at the anterior end 

 of the body-cavity, the space in front of it being occupied partly by 

 muscles and tracheae, and being partly unoccupied. The ventriculus 

 may be seen lying nearly centrally and occupying a large portion of 

 the entire space; the oesophagus proceeding from it forward and 

 slightly downward. The great supra-cesophageal ganglion is seen in 

 the central line near the ventriculus, while the hinder portion of the 

 canal is entirely concealed by the central ovary. A very large 

 Malpighian vessel on each side may be seen, usually filled with white 

 opaque matter. The posterior ends of these tubes are concealed 

 beneath the central ovary, while the vessels run at the side of, or 

 slightly under, the ventriculus, but extend as far forward as the 

 mouth-opening, or even a little beyond its commencement ; and then 

 turn sharply backward so as to fall over the anterior edge of the 

 ventriculus and lie upon it. The larger eggs in the oviducts may 

 commonly be just seen, below all the above-named organs, projecting 

 at about the middle of the ventriculus. The tracheae will also be seen, 

 arranged at first in three principal bundles, and then separating out, 

 as explained below. 



The Alimentary Canal. Figs. 8-9. 



The canal has a great general resemblance to that of the Orihatidw, 

 but is composed of finer and more delicate tissues, which renders it 

 very diflicult to get the whole canal out perfect without breaking it, 

 although there is comparatively little difficulty in dissecting it out in 

 pieces. 



There can scarcely be said to be any pharynx in the sense of an 

 enlarged chamber, such, for instance, as the pharyngeal sac of Huxley 

 in Scorpio ; a hardly perceptible widening of the oesophagus before it 

 enters the mouth-cavity being all that exists ; but if the anterior 

 portion of the oesophageal tube, i. e. the portion to which the dilator 

 muscles for suctorial purposes are attached, although scarcely if at 

 all enlarged, is to be regarded as a pharynx ; which appears to be the 

 mode in which Herr Winkler uses the term in this instance, then of 

 course it would exist, but not be distinctly divided off from the 

 cesophagus. This is practically a question of nomenclature : I have 

 used the word " oesophagus " for the whole, which appears to agree 

 with its use by MacLeod, Henkin, Nalepa, and others, in other families. 



The oesophagus (oe) is long, about half the length of the ven- 



