380 ME. H. M. BEBNAED ON THE 



occurrence in the cephalotlioi'ax, and (3) their absence from the 4th segment and from 

 the abdomen, has hitherto met with no favour. The general opinion, which I am still 

 unable to share, seems to be that they must be regarded as true nephridia *. 



The Malpighian Tubules. — These are well developed in the Galeodidse. They open 

 into the mid-gut in the region of the 4th abdominal segment, one on each side. The 

 apertures are large, as indeed are the main ducts of the glands, and, near the entrance, the 

 epithelium lining them closely resembles that of the mid-gut. It is instructive to note that 

 the entrance is at the point where the fsecal masses commence to form. (PI. XXXIII. 

 fig. 1.) 



The main ducts run forward and backward on each side of the central canal of the 

 mid-gut, somewhat ventrally, to near the diaphragm anteriorly and the stercoral pocket 

 posteriorly. They give off a thick felt of fine tubules which encircles the posterior part 

 of the mid-gut, just before its junction witli the hind-gut, while larger and more important 

 branches ramify among the digestive tubules. The finer branches are less than 10 ^ in 



* I have been severely blamed (Kingsley 36, Laurie 47) for persisting in suggesting that coxal glands may be 

 •derivatives of setiparous glands. I take this opportunity of explaining why I do so in spite of the array of well- 

 known authorities who, on embryological grounds, claim them to be true nephridia. It is quite possible that they 

 are, but I do not think the evidence is sufficient on cither side to admit of dogmatic assertion. They are said to be 

 mesodermal in origin, but the endosternite and the stercoral pocket have also been claimed as derivatives of the 

 mesoderm. These latter appear to me as very good illustrations of the great difficulties which lie in the path of the 

 embryologist. The study of Galeodes shows beyond doubt that the endosternite is an infolding of the cuticle, and 

 the stercoral pocket is an outgrowth of the chitin-lined hind-gut. In the same way, the difficulties in investigating 

 the developing coxal glands are very great. In the adult animal the aperture of the gland is by no means easy to 

 find. It was long thought that there was no aperture in the adult Scorpion, and I have only found the aperture in 

 Galeodes in two specimens. The investigation cannot, therefore, be an easy one. 



On the other hand, I do not think that my suggestion involves any great morphological heresy, but, on the 

 contrary, it is, under the circumstances, a very natural one. It arose out of my endeavour to show in detail how 

 Apvs could be deduced from a chietopod Annelid (4, see also " Systematic Position of the Trilobites," Quart. .Tourn. 

 Geol. Soc. vols. 1., li.). The primitive Crustacea should therefore have originally possessed tufts of setae on both 

 the dorsal and ventral branches of the limbs. On the ventral branch such tufts may perhaps be found in the 

 tooth-like bristles of the guathobases ; but on the dorsal they are now scattered, or vanished. This assumption has 

 recently been amply justified. In the Trilobite Triarihnis Beclcii, tufts of setae have been found on the dorsal 

 branches of head-limbs answering well to those which I postulated for the immediate ancestors of Apus. These 

 tufts have vanished from the vestigial dorsal branches of the head-limbs of A2ms, but we find instead glands, in all 

 three pairs, which seem to me more likely to be derivatives of setiparous glands than of nephridia. There is some 

 reason, indeed, for believing that it is especially when parapodial appendages degenerate (see pp. 403-404) that the 

 glands of their supporting acicula become modified for other uses. 



The 1st gland belongs to the 1st segment, and in its structure is very like a setiparous sac, still attached by 

 muscles to the body-wall. It opens on each side into the mouth-aperture (4). This I would attribute to an acicular 

 gland of a vanished parapodium of the 1st segment. 



The 2nd gland opens on the base of the 2nd antenna ; it is only developed as a gland in the young Ajnis (Glaus), 

 but degenerates in the adult. In the higher Crustacea it persists as the antennal gland. Its position is not clear, 

 because the morphology of the limb is not yet understood. The basal swelling on which its aperture persists in 

 Apux is difficult to homologize with any part of a typical parapodium. 



The 3rd gland opens upon the vestigial remains of the dorsal branch of the parapodium of the 5th segment, 

 where we now know from TriartJiriis that a tuft of setaj once existed. It develops into the shell-gland. 



These three glands appear to form a series, of which the 1st, by its structure, suggests a modified setiparous gland, 

 and the last by ts position on the dorsal branch of a limb where we know that a tuft of setiB once existed. 



