446 GEPHYREA 



animals they attempt to describe, and they should be given up. 

 Both names had reference to the presence or absence of the two 

 hook-like bristles described on the ventral surface of some of the 

 Echiuroidea, but of the five genera of this family, two, Saccosoma 

 and Hamingia (the latter in the female or normal form), are 

 without these bristles, and can therefore be described neither as 

 Armaia nor as Chaetifera. On the other hand, hook-like chitinous 

 bristles of somewhat the same nature, though smaller in size and 

 varying in position, are very common on the introvert of Sipun- 

 culoidea and on the body of the Priapuloidea. 



Again, the association of the two last-named Orders in one 

 sub-group is, to my mind, an error. The Priapuloidea have 

 little in common with the Sipunculoidea ; almost the only 

 real point of resemblance is the power of protruding the. 

 anterior part of the alimentary canal, and withdrawing it 

 by the aid of retractor muscles. But in the Priapuloidea this 

 power exists to a very small extent, and it is a power shared by 

 very many animals besides the Gephyrea. The terminal anus 

 of the former is a feature shared by the Echiuroidea and by 

 Epithetosoma, but these have little else in common with the 

 Priapuloidea. On the other hand, the entire absence of any 

 head appendages, such as the proboscis of the Echiuroidea and 

 the tentacles or tentacular membrane of the Sipunculoidea, the 

 absence of a vascular system, of nephridia or anal vesicles, taken 

 together with the straight intestine which occurs elsewhere 

 only in Epithetosoma, the persistent connexion of the nervous 

 system with the epidermis, the unique character of their excretory 

 system and of the reproductive organs, are all features in which 

 the Priapuloidea differ from the more normal members of the 

 other three Orders. These constitute a list of peculiarities which 

 are at least as important, and probably even more important, than 

 those which characterise the Sipunculoidea and the Echiuroidea. 

 Thus the Priapuloidea should, I think, be regarded as a distinct 

 Order, which occupies a very isolated position in the group. 



Until we know something about the development of Hali- 

 cryptus and of Priapulus, it will be difficult to say whether the 

 Order is more nearly allied to one or the other of the two great 

 Orders of Gephyrea, whether it is very primitive or very 

 specialised. The connexion of the entire nervous system 

 with the epidermis and the absence of a vascular system are both 



