﻿PVCXOGOXIDA. jQ 



examinations of the development of the Pycnogonida seem to me to show that in these animals the 

 separation of the nerve mass into ganglia only takes place by degrees, conteniporaneouslv with a 

 corresponding separation of the somites of the trunk, and the separation and growth of the limbs, 

 comp. m>- figures of the first lar\al stages in XyDiplinu iii(icro)iyx, pi. 11, fig. 9, Psrudopallrnr circularise 

 pi. I, fig. II, and Xxiiiplion Sliiilrri, pi. II, fig. 18, and with these figures may be compared the abdom- 

 inal ner\-e cord in Pscitdopnllciie circular is in the second and [third lar\al stage, pi. I, fig. 12 and 15. 

 Upon the whole I doubt very much that a coalescing of well separated limbs really takes place, and 

 so much 1 know at all events from my own examinations that the union, supposed to take place of 

 the arms of the second pair of feet in the females of Lerujeopoda to a fastening knob, is only 

 apparent, each arm in reality ending in an independent knob; the two knobs are onlv more or less 

 loosely joined to a single knob — by a somewhat strong pressure the^■ are easih- separated. As a 

 paradigm on the coalescing of limbs this pair at all e\-ents cannot be used. 



The proboscis is thus, after its origin and structure, especially the want of limbs, not 

 homologous with the other metameres of the body; but even if it be .something particular, or, to use 

 the expression of Dohrn organum sui generis , it can in no way be said of it, as does this author, 

 that im ganzen bisherigen Arthropodentypus nicht seines Glcichen, nicht einnial etwas ihm Aehn- 

 Hches is found, Pantop. Golf. Neap. iSSi, p. 13, for I suppose that the proboscis of the Pycnogonida 

 will be found throughout the class of Arachnida, the only difference being that here it is free, large, 

 and jjredominant, while in the other Arachnida it most frequently is very small and hidden between 

 the gnathites. As an instance of a free proboscis in the Arachnida I shall refer to what in the follow- 

 ing is said of the genus Kocneiiia. As I have already indicated in the foregoing, in the chapter on 

 the terminology, p. 3, there is still less reason to interpret it as, or give it the name of, head. A 

 similar structure of the mouth is otherwise found in some mites, as it also in several respects reminds 

 of the mouth in some higher, sucking worms {Hiritdo). In the Insecta, especially in the Tipulida, we 

 find a parallel in the structure of the gullet; and as well in the Pvcnogonida as in the Tipulida the 

 production of a pumping or sucking apparatus may be thought to be the conditional reason of the 

 common plan of structure. I think it ma\' be taken ti.i be a consequence of simple, mechanical laws 

 that, when a tube with firm walls is to form a pumi:)ing or sucking apparatus, the ea.siest thing will 

 be to place three jjlates with contiguous margins longitudinally in the the tube, and b\- ropes or 

 other suitable means make those plates to approach the wall of the tube at the same time, 1)\- which 

 motion the inner opening will be increased, and a pumping or sucking be brought about. A\'illi 

 regard to the Tipulae I may refer to ni}- paper. The Gnathites of the Flies. Trophi Dipterorum 

 (1881). On pi. II, fig. 10 of this paper is found a tran.sverse .section of the gullet of a Tijiulid of the 

 triangular form, so well known from a number of figures and transverse sections of the proboscis of 

 the P\cnogonida. 



For the elucidation of the nujrphological significance of the proboscis I may also refer to the 

 figures in a recent work by two Danish zoologist.s, the doctors H. J. Hansen and Will. Sorensen: 

 •The Order Palpigradi Thor. (Kocnenia mirabilis Grassi) and its Relationship to the other Arachnida 

 (1898). This Arachnid has already earlier been the sul)ject of a detailed examination and a systema- 

 tical view by Grassi: I Progenitori dei Miriapodi e degli Insetti. Memoria \'. Intorno ad un muno 



