COMPARATIVE MOEPHOLOGT OF THE GALEODIDJi:. 381 



diameter. Whether the ramifications anastomose I liave not been able to discover. 

 The tubules themselves are very irregular, the terminal portions swelling into irregular- 

 shaped knobs or vesicles. 



It is important to note that these ramifying excretory tubes are confined to the 

 digestive mass ; at least, I can find no trace of them projecting beyond, /. e. into the 

 blood-spaces under the skin. The peristaltic action of the muscular tunic of the 

 alimentary canal and diverticula Avould produce a certain waste which would have to be 

 removed. 



The Malpighian tubules are formed of a very low, finely ciliated epithelium (except 

 near their apertures, where they continue the character of the mid-gut epithelium), with 

 large round or oval nuclei, 2-3 /i in diameter. The epithelium rests on a granular 

 membrane, which appears to blister off from the epithelium so as to form small lacunse 

 between it and the cells. This seems not to be the case everywhere, but where it occurs 

 gives the impression of being a normal and not a pathological or post-mortem phenomenon, 

 as the cells do not break away from the membrane altogether, but remain attached, 

 I only observed this on portions of the tubes dissected out and examined in tofo. As 

 in the coxal gland, the contents of the interior appear as masses of clear round or oval 

 vesicles with slightly granular envelopes. These excreted vesicles do not show the same 

 close resemblance to the nuclei of the lining cells as do the vesicles in the lumen of the 

 coxal glands, although appearances in favour of a similar origin were not altogether 

 A\anting. This whole subject requires new and extended investigation on better 

 preserved material, and conducted solely with the one object of discovering whether the 

 discharge of nuclei in excretory processes is the true explanation of the phenomena. 



In Scorpio, the Malpighian vessels arise at the boundary between the mid- and hind-gnts, where the 

 faecal masses appear to form (in the 7th abdominal segment), and no doubt, as in Galeodes, belong to 

 the mid-gut. They arise close to each other on the dorsal wall, and run straight forward on the dorso- 



Further, (1) the well-known progressive backward degeneration of the anterior nephridia in Annelids, and (2) the 

 «laim that the chitinogenous cells utilize excretory matters in the formation of the cuticle, are additional arguments 

 in favour of the deduction of the antennal and shell glands of the Crustacea from setiparous glands. The secondary 

 opening of ectodermal invaginations into internal spaces is so common an occurrence that it presents no serious 

 difficulty. 



On turning to the Arachnids, the general resemblance between the coxal glands and the antennal and shell glands 

 of the Crustacea is sufficiently striking. Might thej- not also be setiparous in origin? They appear to belong 

 to the same series as the traeheae and spinning-glands, and are always associated mth limbs. This hypothesis, 

 further, best explains their singularl}- limited distribution. 



I freely admit that these arguments would have but Httlo weight as against direct embryological evidence, if 

 that evidence were reaUy satisfactory. But, apart from the difficulties of observation above noted, the evidence from 

 embryology does not appear to me to he conclusive. For instance, if setiparous sacs could become specialized for 

 excretory purposes into complicated organs no longer purely ectodermal, there is no way of knowing whether the 

 course of the development of such organs repeats its ph3logenetic history or whether the definitive form is not at onee 

 laid down. In the Arachnids, which have no larval stages, each appearing with its definite characteristics even 

 in the egg, it seems to me highly probable that all the more important organs are laid down in their definite 

 form at their first appearance, and that their ontogeny teaches us but httle of their phylogenetic history. For this 

 reason I cannot follow Kingsley in being satisfied with the embryological evidence. I believe that the ultimate 

 decision rests with comparative anatomy. 



