ARTHROPODA OF DOUBTFUL POSITION. 



79 



A short oesophagus opens into a muscular enlargement, the walls of which are lined 

 with chitinous projections, the whole presenting a strong resemblance to the anterior 

 portion of the stomach of the lobster. From 

 this stomach a tube of varying length goes 

 to the anus. From this tube arise elongated • 

 pockets or coeca, varying in number from four 

 to six pairs, which enter, to a greater or less 

 extent, the proboscis, mandibles, and legs. 

 The heart is a short tube, which has usually 

 three incurrent apertures, while the blood 

 by its action is forced forward through an 

 anterior excm-rent orifice into the spaces be- 

 tween the muscles and the viscera, there 

 being no arteries or aorta present. Respira- 

 tion is effected through the general sm'face 

 of the body, there being no specialized organs 

 for the purpose. 



The sexes are always separate. The gen- 

 ital organs are lodged in the ambulatory legs, 

 ahd have their openings in the basal joints. 

 The eggs are impregnated after emission, and 

 are transfeired to the ovigerous legs of the 

 male, where they are enveloped in small sacs, 

 and usually, hatch with the proboscis, palpi, mandibles, and three pairs of legs devel- 

 oped, though some species have only one pair fully developed, and others have four 



Fig. 108. — Galls and youns 

 enlargec 



of Plioxichilidium, 



The eggs undergo a total segmentation. 



Fig. 109. — Colossend^s eoloseea, one-half natural size. a. Palpi, d. Probosoie. I, Legs. o. Ovigerous legs. 



at the time of leaving the egg. The young of the genus Phoxichilidium live a semi- 

 parasitic life within the digestive cavities of certain tubularian hydroids, where they 

 form what may be called galls. 



Pycnogonids are not rare on our coasts, and may be sought for on Carnpanularim 



