MOEPHOLoaiCAL METHOD AND RECENT PROGRESS IN ZOOLOGY. 003 



eliiiiiiiatioii oi' tliosc chanjicters which arc found to he least con- 

 stant. And necessary is it, aho\e all thino-.s, that in institutino- com- 

 parison it should he tirst ascertained wh .t it is that constitutes a 

 crustacean, a niarsipobranch, a c^^clostonie, and so on for the rest. 

 We have tried to acc(>pt this theory, fascinated both by the arguments 

 employed and by the idea itself, which for inuenuit}' it would be ditti- 

 cult to ])eat, but we can not; and we dismiss it as misleading, as a 

 fallacy, ])eg-otteh of a misconception of the nature of the morphologi- 

 cal method of research. It is of the order of events which led Owen 

 to compare a cc[)halopod and a verte})rate, led Lacaze-Duthiers to 

 regard the Tunicata and Lam(dlibranchs as allied; and with these and 

 other heresies it must he denounced. 



Passing to the third advance, extending over the last twenty years, 

 it may be said to consist in the revival of a theory of 182!), which 

 })oldly asserts that Linudus is an Arachnid. In the development of 

 the d(>fense there have l)een two weak points ])ut lately strengthened, 

 viz, the insufiicient consideration of the pal(\?ontological side of the 

 ([uestion and of the presence of trachea^ among the Arachnida. Under 

 the former there was, until recently, assumed the a])sence of the tirst 

 l)air of appendages in the Eurypterida; but it may be said that they 

 have since been observed in E'>/r>/j)ft i'l/s p'sr/u't'/ of the Russia Silurian, 

 and K KCoticK^t from the Pentland Hills, in both of which they consist 

 of small chelate appendages Hexed and llmuloid in detail, somewhat 

 reduced perhaps, and inclosed by the bases of the succeeding limbs, 

 which l)ecome apposed as the anterior end is reached. Since by this 

 discovery the Limuloids, Eurypterids, and Scorpionids are 1)rought into 

 a numerical harmony of limb-])earing parts, we may at once proceed 

 to other points at issue. So far as the broader structural plan of Lim- 

 ulus and the Scorpion are concerned, all will agree to a general com- 

 munity, except for the organs of respiration; but concerning the 

 c(clom, the mobile spermatozoa, and the more detailed features under 

 which Lumdous is held to diti'er from the Crustacea and to resemble the 

 Arachnida, I would remark that while motile spermatozoa are charac- 

 teristic of the Cirripedes, the rest of the argument is weakened, by the 

 prol)ability that the "arachnidan''' characters which remain may well 

 have ])een possessed ])y the crustacean ancestors, and that Limulus, 

 though s])ecialized, being still an ancient form, might have retained 

 them. The difficulty does not seem to mo to li(^ in this, nor with the 

 excretory organs, if we are justified in accepting the aforementioned 

 argument that tli(» so-called Malpighian tubes may be inturned neph- 

 ridia, ectodermal in origin, and in knowledge of the existence of 

 endodermal excretory diverticula in the Amphipods. Thes(» facts 

 would seem to suggest that as our experience widens, diflerenccs of 

 this kind will disappear. 



