394 THE ANATOMY OF INVERTEBRATED ANIMALS. 



"head," is attached by a slender tendon to the "mandible" 

 on the one side of the hinge line, while a smaller divaricator 

 muscle is fixed to the other side. The mechanism of adduc- 

 tion and divarication of the mandible is quite similar to that 

 by which the dorsal valve of the shell of an articulated Bra- 

 chiopod is moved upon the ventral valve. 



Male and female reproductive organs are usually com- 

 bined in the same polypide. They are cellular masses, devel- 

 oped in the funiculus, or in the parietes of the body, whence 

 the ova or spermatozoa are detached into the perivisceral 

 cavity. They sometimes pass thence, and undergo the first 

 stages of their development in dilatations of the wall of the 

 body, termed ovicells. 



Multiplication by gemmation occurs throughout the group, 

 but the buds usually remain adherent to the stock. In Loxo- 

 soma and Pedlcelluia, however, the buds become detached. 



Some Polyzoa multiply agamogenetically by a kind of 

 gemmule developed in the funiculus, provided with a pecul- 

 iar shell, and termed a statoblast. 



With these general characters, the Polyzoa present an 

 interesting series of modifications. They have been divided 

 by Nitsche into two groups — the Entoprocta, in which the 

 anus lies within the circle of tentacles ; and the Ectoprocta, 

 in which it lies outside this circle. In the former division, 

 the genus Loxosoma, 1 which attaches itself to Sertularians 

 and to other Polyzoa, is particularly noteworthy. It is a 

 small stalked animal, and the superior wider end of the body 

 is an obliquely truncated disk, the margins of which are elon- 

 gated into ten ciliated processes. The mouth is a trans- 

 versely elongated, slit-like aperture on the lower side of the 

 tentacular circlet. A long oesophagus connects this with a 

 globular cascal gastric sac. From the midst of the disk, a 

 conical prominence, the summit of which bears the anus, is 

 situated. The sexes are united, the ovaries and testes being 

 situated on each side of the stomach, and the spermatozoa 

 pass directly into the ovaries. No nervous system has yet 

 been made out in Loxosoma. The animal is fixed by the 

 truncated extremity of its narrow stalk-like end ; and this 

 stalk contains a gland, the duct of which opens in the centre 

 of the face of attachment. 



Loxosoma appears to multiply by budding, but the ap- 



1 Kowalewskv, " Bcitrage zur Anatomic und Entwickelungsgeschichte des 

 Loxosoma neapolitanum " ("M6m. de l'Acad. de St.-Petersbourg," 1866). Os- 

 car Schmidt " Die Gattung Loxosoma" ("Archiv liar mikr. Anatomie," 1875). 



