ANARTHROPODA. 469 



(and possibly even the Laurentian) deposits contain the remains of 

 animals belonging to this division. Finally, the division of the 

 Scolecida comprises the various " Worms " which from their com- 

 monly parasitic habit are generally known as the Entozoa, together 

 with the group of the Wheel-animalcules or Rotifera. To say noth- 

 ing of the microscopic dimensions of the Rotifers and many of the 

 Entozoa, none of the Scolecids are provided with hard structures, 

 which, under ordinary conditions, could possibly be preserved in the 

 fossil state. It would, therefore, be no matter of surprise to find 

 that we have absolutely no record of the existence of these animals 

 in past time. There are, however, a few remains which have been 

 referred to the Entozoa, and which may be noted here. The most 

 satisfactory of these is a worm which was found by von Heyden in 

 the abdomen of a fossil Beetle from the Miocene Brown Coal of 

 Germany, and which has been referred to the Hairworms (Gordiacea) 

 under the name of Mermis antiqua. The same genus has been 

 detected in amber, along with minute filamentous worms which 

 have been referred to the Nematoda, and have been placed under 

 the genera Anguillula and Enchytrceus. These are the sole remains 

 of Scolecids which have hitherto been detected, and it is there- 

 fore unnecessary here to deal further with this division of the 

 Annulosa. 



Anarthropoda. 



The animals included in this section are usually spoken of as 

 "Worms," and constitute the highest division of the " Vermes" as 

 this name is now understood. Under this head are placed the 

 Spoon-worms (Gephyrea), the Arrow-worms (C/uztognat/ia), and 

 the Ringed Worms (Annelida), together with the small and aberrant 

 group of the Myzostomida. The division is characterised generally 

 by the usually elongated, vermiform body, which is, typically, com- 

 posed of numerous, clearly recognisable segments. The segments 

 are in general nearly similar : and when lateral locomotive appen- 

 dages are developed, these are not composed of successive joints, 

 and are not articulated to the body. 



Of the four groups included under the head of Anarthropoda, 

 the Annelides are comparatively well represented as fossils, com- 

 mencing in the Cambrian period. On the other hand, the Chcetog- 

 natha are wholly unknown in the fossil condition ; as also are the 

 Gephyreans, unless Ehlers be correct in referring to this group 

 certain obscure remains from the Lithographic Slate (Jurassic) of 

 Germany, for which he proposed the name of Epitrachys. The 

 Myzostomida, however, have been certainly recognised in the fossil 

 condition, though their geological history is still imperfectly known. 

 Myzostoma, the type-genus of this curious and abnormal group, 



