THE CESTOIDEA 



is known only from Leuckart's observations on preserved material This 

 worm is stated to become sexually mature in the Oligochaete, and would 

 be remarkable, firstly, for being the only Cestode inhabiting a single 

 host, and secondly, in that host being an Invertebrate. The genital 

 organs (see 1 5) appear to be identical with those of Caryophyllaeus, and it 

 is desirable to have further information about the character of the " head,''' 



Fio. I. Caryophyllaeus mutabilis, Rud. 



1. Mature worm from the intestine of the roach, Ltuciscus rutUus. (x7J, orig.). The 

 general disposition of the genital organs is shown, a, mobile organ ; c, cirrus ; g, germarium ; 

 t, testes ; v, vitellaria ; u, uterus, the coiling of which has been simplified ; v, vagina ; x, ex- 

 cretory pore. The male duct opens into the atrium (the outline of which is unfortunately 

 indistinct) opposite to the vagina, and the uterus opens also into the atrium, close to the latter. 

 The atrial pore is not lettered, but is seen in line with the letter tt. 



2. Immature worm removed from the coelom of the genital segments of Tubifex rivul- 

 orum. (x!5, orig.). It still retains its "caudal vesicle," which is armed with six booklets. 

 This specimen is a small one ; others occur in the Oligochaete of the same size as, or even 

 larger than some specimens found in the fish, and frequently have the genital organs fully 

 fonned, but without eggs. 



8, 4, 5. Outline of the mobile organ in three stages of forward movement 8, at the begin- 

 ning, and 5, at the terminal stage of the process. During this movement of the mobile organ, 

 a wave of contraction passes forwards along the body, so as to bring the whole animal forwards. 



for in preserved specimens of the latter genus, an appearance, not unlike 

 that figured by Leuckart, is presented. It is, moreover, to be noted that 

 the genital organs of Caryophyllacus are fully developed while it is still 

 provided with a " caudal vesicle " and inhabiting the body of Tubifex. 



Remarks upon the Monozoa These unisegmental Cestodea 

 exhibit undoubted affinities with the Trematodes, and especially 

 with the Heterocotylea. A re'sume" of the anatomy of the genera 



