292 



ZOOLOGY. 



not yet solved, and in the meantime another source of food is likely to be 

 destroyed through overfishing. 



The cray-fish is prized for food in European countries, but is little used 

 in America as yet. Shrimps, prawns, the " soft-shelled " or blue crab are 

 all of considerable importance in this regard. The smaller Crustacea are 



FIG. 133. Caprella geometrica. From Verrill. x 4. 



Questions on the figure. In comparison with other Crustacea what 

 are the aberrant or peculiar features of this form? See also figures in 

 reference texts (e. g., Parker and Haswell's Zoology, Vol. i, p. 546). 



a very important element in the food supply of the fishes, both in the fresh 

 waters and in the sea. 



Class Il.-Onychophora. This class of arthropods includes only the 

 one genus, Peripatus, which is interesting chiefly because it is, in some 

 degree, intermediate between the Annulata and the higher arthropods. 

 There are about a dozen species of Peripatus, chiefly from Africa and 

 South America. They are found in moist places, under wood, stones, and 

 in rotting bark. They agree with the chsetopod annulates (see 270) in the 

 possession of segmental organs (nephridia), a dermo-muscular sac, and 

 poorly developed appendages. The segments are also homonomous (see 



FIG. 134- 



FIG. 134. Peripatus capensis. From Nicholson after Moseley. 



Questions on the figure. Externally in what respects is this form like 

 the Annelids? In what respects different from them? Of what special 

 zoological interest is this genus? What are its habits? In what respects is 

 it like and in what unlike the centipede (Fig. 135) ? 



258) as in the worms. The relationship to arthropods is indicated by the 

 possession of tracheae, by the substitution of haemocoele (the enlarged 

 lacunae in which circulation occurs) for the true crelom, and by the 

 differentiation of some of the anterior segmental appendages as mouth 

 parts. The Onychophora resemble the larval condition of those insects 

 which undergo a metamorphosis much more than the adult stages. This 



