Characteristics of Rotifera. cxxxix 



main organ of locomotion. The ingestion of food is dependent npon 

 the agency of the same organ^ on the ventral aspect of which it 

 almost always lies ; though the anterior portion of the digestive 

 tract is protrusible in the Rotifera^ as in the most typical Annulata. 

 In the male Rotifera the digestive tract is entirely absent, or repre- 

 sented only by a rudiment of an oesophagus. In the females of 

 certain orders^ the digestive system consists merely of an oesophagus 

 and a coecal stomach, as in Ascomorpha, Notommata^ Asplanchna ; 

 whilst in others it possesses a proctuchous intestine which ends in a 

 cloaca, together with the outlets of the water- vascular and oviducal 

 apparatus. A gizzard armed with chitinous^ often com^^lex, 

 characteristic jaws is interposed in all female Rotifera between the 

 mouth and the stomach ; two or more coecal appendages are affixed 

 to the commencement of this latter organ^ which^ as also the in- 

 testine, is clothed internally with cilia. 



The Rotifera have no heart; the j)erivisceral cavity contains a 

 corpusculated fluid. There are no specialized respiratory organs. 

 The water-vascular depuratory system has a great development, 

 taking the shape of symmetrical tubes, which open inferiorly into the 

 cloaca, and ordinarily^ after entering an azygos contractile vesicle ; 

 and which have appended to them, peripherally at least, as many 

 as five ciliated infundibula opening into the perivisceral cavity. 



The nervous system consists of a bilobed ganglionic mass, which 

 is placed above the oesophagus, but does not throw a collar round 

 it. One or two eye-specks are sessile upon this ganglionic mass ; 

 and certain spots beset with non-mobile bristles, as well as a tubular 

 process, the so-called 'respiratory tube,^ are, inasmuch as they 

 receive nerves carrying ganglioniform intumescences, to be re- 

 garded as being probably sensory organs. 



The Rotifera are dioecious. The males, besides possessing no 

 digestive tract, and living therefore but a short time, differ from 

 the females in their external appearance ; in their much smaller 

 size ; and in their much smaller numbers. The testis and ovary are 

 azygos glands, and have their external walls continuous with those 

 of the efferent ducts, opening at the posterior boundary of the body 

 proper, anteriorly to the ' foot ' or * tail ' when present, and on the 

 dorsal surface. Reproduction takes place by means of two kinds of 

 ova, the ' summer^ and the ' winter ova.' Of those, the former are 

 agamogenetic, like the summer ova of the Daplmidae and Cladocera 



