9O THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. 



that most of the smooth trilobites are punctate, some of them very conspicuously so, and 

 the spines and pustules of ornamented trilobites may merely subserve the same function as 

 the pores of smooth ones. 



If the spines were protective, it would not be surprising if some of them, hollow and 

 open at the top, were poisonous also, and had glands at the base. These are, however, 

 purely matters of speculation so far. 



Renal excretory organs. Nothing has been seen of any such organs, unless the genal 

 caeca may possibly be of that nature. The main trunks of these always lead to the sides 

 of the anterior glabellar lobe, which is not the point of attachment of either antennae or 

 biramous limbs, so that there seems little chance that they will bear this interpretation. 



Reproductive organs. Nothing is yet positively known about the reproductive organs 

 or the position of their external openings. If the "exites" of Neolenns could be interpreted 

 as brood-pouches, which does not seem probable, then the genital openings were located near 

 the base of some pair of anterior thoracic appendages. 



The Panderian Organs: Internal Gills or Poison Glands? 



At a meeting of the Mineralogical Society at St. Petersburg, Volborth (1857) announced 

 that Doctor Pander had two years before discovered certain organs on the lower side of 

 the doublure of the pleural lobes of the thorax of a specimen of Asaphus expansus. These 

 organs were oval openings in the doublure, one near the posterior margin of the cephalon, 

 and one on each thoracic segment of the half-specimen figured by Volborth in 1863. They 

 were explained by Volborth and by Eichwald (1860, 1863) as the points of attachment of 

 appendages. Billings (1870) described and figured the "Panderian organs" of "Asaphus 

 platycephalus" and stated that he had seen them in Asaphus [Ogygites] canadensis and 

 A. megistos [Isotclus maximus\ as well. He thought some sort of organ was attached to 

 them, but could not suggest its function. Woodward (1870) thought that the openings were 

 "only the fulcral points on which the pleurae move." Their position outside the fulcra shows 

 that this explanation is impossible. 



So far as I am aware, the Panderian organs have been seen only in the Asaphidas. 

 Barrande figured them in "Ogygia" [Hemigyraspis] desiderata (1872) and Schmidt in two 

 species of Pseudasaphus. They seem to occupy the same position in Bohemian, Russian, 

 and American specimens. There is always one pair of openings on each thoracic segment, 

 and one pair in line with them on the posterior margin of the cephalon. They occur near 

 the anterior margin of the segment, and near the inner end of the doublure. In some cases 

 they are surrounded by a ventrally projecting rim, while in others they have a thin edge. 

 There seem to be no markings on the interior of the shell which are connected with them. 



While thinking over the trilobites in connection with the origin of insects, it occurred 

 to me that these hitherto unexplained Panderian organs might possibly be openings to internal 

 gills and that the Asaphidse might have been tending toward an amphibious existence. On 

 mentioning this to Doctor R. V. Chamberlin of the Museum of Comparative Zoology, he 

 called my attention to the possibility that they might be openings similar to those of the 

 repugnatorial glands of Diplopoda. While no definite decision as to the function can be 

 made, the explanation offered by Doctor Chamberlain seems more plausible than my own, 

 and has suggested still a third, namely, that they might be the openings of poison glands. 



If one were to argue that these apertures are really connected with respiration, it might 

 be pointed out that they are ventral in position, while the foramina repugnatoria are always 



