60 VERMES. 



Ichthydium (worm-shaped, with a ciliated ventral surface) is 

 by some referred to the Botifera ; Metschnikoff forms for it an 

 order Gasterotricha. Schmarda, the more recent authority, 

 places it in this order, and he also includes in it " Polyophthal- 

 mida," Maldanidge ( = Clymenidce), and Chaetopteridae. With the 

 two following orders they form his sixteenth Class Chaetopoda 

 ( Van Benederi). He estimates that these three orders contain 

 1500 species. 



Ichthydiidce. Enchytrceidce. Lumbricidce. 



Ichthydium. Enchytraeus. Lumbricus (Earth- 



Chastonotus. Chastogaster. worm). 



Dero=Proto. Perichaeta. 



.ZEolosoma. Scenuridce. Phreoryctida. 



Nais=Stylaria. Sagnuris=Tubifex. Phreoryctes. 



Aulophorus. Euaxes=Khynchelmis. Megascolex. 



Limnodrilus. 



Order III. CHJETOPODA. 

 ERRANTIA. ANTENNATA. POLYCH^TA. EAPACIA. NOTOBRANCHIATA. 



Marine animals, mostly worm-like, with tubular setigerous 

 feet [parapodia]. Body not presenting distinct regions. Meta- 

 morphosis in most. 



The sexes are mostly distinct, but asexual forms occur giving 

 rise to the former; "a process of zooid development" takes 

 place which " appears to be a combination of fission with gem- 

 mation ;" and " the result is, not infrequently, the formation of 

 long chains of connected zooids." The males and females, in 

 some cases, differ from one another as well as from the sexless 

 forms. The young, on leaving the ovum, is a free-swimming 

 ciliated body. SyUis, Eunice, and a few others are said to be vivi- 

 parous. 



The branchiae are external and ranged along the side of the 

 back ; but in many the branchiae are rudimentary or absent, and 

 the respiration is either carried on by the skin or by sea-water 

 admitted to the peri visceral cavity : mixed with chyle, this fluid 

 is known as the "chylaqueous fluid." According to Owen it 

 serves the place of an internal skeleton by acting as the base of 

 resistance to the cutaneous muscles, "the power of voluntary 

 motion being lost when the fluid is let out." The blood-vascular 

 system is sometimes in abeyance. The blood is red in most, but 



