456 



ARTHROPODA. 



feet are glands recalling nephridia in their history. It is possible that 

 these animals are to be placed among the Coelhelminthes. Macrobiotus* 



Pycnogonida (Pantopoda). 



These marine animals have a cylindrical body, with a tubular probos- 

 cis in front and an abdominal appendage behind, and four pairs of very 

 long legs. In front of the legs is a pair of small chelate appendages and 

 usually a pair more like pedipalpi. In the male there is an additional 

 pair of ' ovigerous ' legs to which the eggs are attached after being 

 deposited by the female, thus giving a total of seven appendages, a num- 



FIG. 476. Nymphon stroemii * (orig.). c, chelicerse ; o, ovigerous legs ; p, pedipalpi ? 



r, rostrum. 



ber not reached in any arachnid. Diverticula of the stomach extend into- 

 the legs ; a heart is present, but respiratory organs are lacking. The- 

 Pycnogonids, which creep slowly over seaweeds and hydroids, may be (1) 

 a distinct group of arthroproda, or (2) modified arachnids, or (3), and less 

 probable, Crustacea. Nymphon* Phoxichilidium* Colossendeis.* 



Class III. Malacopoda (Protracheata). 



These forms, including only a single family PERIPATID^E, show 

 a strange mixture of annelid and arthropodan (or ' tracheate ') 



Fio. 477. Peripatus capensis. (From Balfour, after Moseley.) 



characters, so that they are usually regarded as representatives of 

 the stock, early separated from the annelids, from which the Insecta 

 have descended. They recall the annelids by the presence of 

 nephridia, so characteristic of that group, which begin by a closed 

 vesicle (reduced coelom), pursue a short course, and expand into a 

 urinary bladder before opening at the bases of the legs (fig. 478, 

 so). On the other hand they possess tracheae, long unbranched 



