PYCNOGONIDA OF NEW ENGLAND AND ADJACENT WATERS. 465 



cies, according to Zenker, liorny denticles by which food niny be still 

 further comminuted. The homologies of the rostrum are not well 

 understood. It is regarded by Huxley as representing the coalesced 

 chelicera3 and pedipalpi, like that of the Acarina; and Latreille states 

 that in a large species of PhoxicMhis from the Cape of Good Hope he 

 found longitudinal sutures in the rostrum, so that it appeared as if con- 

 sisting of the ''Labrum, lingua and two jaws united together." Other 

 writers have regarded it as the head, etc. It seems to me that a study 

 of the embryology does not confirm these views, for the rostrum in its 

 early stages x)resents no trace of sutures or other evidence of its com- 

 posite nature, but arises as a simple protuberance between the bases of 

 the antennie. Posterior to the antenniie, and at the sides of the rostrum, 

 are, in many genera, a pair of so-called ' jjalpi,' which are composed of 

 five to nine joints, and are sometimes furnished with plumose hairs that 

 undoubtedly have a tactile function. The third pair of appendages, 

 which are wanting in the females of certain species, have been termed 

 'ovigerous legs,' from their ofl&ce, in the male, of bearing the egg- 

 masses, it having been formerly supijosed that the females never i)OS- 

 sessed them. This term is, however, inappropriate when applied to the 

 female appendages, and it seems preferable to term them accessory legs, 

 as certain writers have done, at least until their homologies are better 

 understood. The legs proper are eight in number, and are, as already 

 mentioned, remarkable in many species for their great length. They 

 are composed of nine joints, of which the last, or dactylus, is claw -like 

 and forms, in some species, a sub-cheliform hand with the i^receding 

 joint or propodus. In certain genera the dactylus is armed with two 

 movable auxiliary claws, articulated to its upper side near the base; 

 their presence or absence forms a valuable generic character. 



The stomach always sends out long prolongations iutp the legs and 

 antennoe, and sometimes, also, rudimentary ones to the palpi and acces- 

 sory legs. These diverticula exhibit active peristaltic movements, which 

 drive the food rapidly back and forth and thoroughly distribute it. The 

 movement is plainly visible in some species of NympJion, and is an inter- 

 esting sight. The stomach-walls contain numerous muscular fibres and 

 are somewhat glandular, but no liver or other special secretory organ is 

 known to exist. The circulatory system is very simple and has beeii 

 detected in only a few species. It consists of a tubular dorsal vessel, 

 with lateral paired openings for the ingress of the blood. Claparede 

 figures in '■'■ Phoxicliilidium'''' cheliferum a distinct aorta, which divides 

 anteriorly into two trunks, emptying into the b6dy-cavity. I have ob- 

 served in Nymiilion grossipes a dorsal pulsating organ, which I believe to 

 be the heart. In the same specimen the perivisceral circulation was also 

 seen. JS^o special respiratory organs have been observed with certainty, 

 though Plianodemus and Oomerus were described as possessing tracheal (?) 

 openings; it seems improbable that this is their true nature, more 

 especially since the tracheae which should communicate with them have 

 30 P 



