274 



NATURAL HISTOET. 



or through perforations in the stem partitions, link one Moss-animal to its neighbours, and thus unite 

 the whole colony in a common life. The endosarc was at first considered to be the colonial 

 nervous system, and to be associated with the singular phenomena of the regular and com- 

 bined movements which occasionally agitate all the members of the same colony. But the 

 researches of Joliet have proved that the tissue is not nervous in structure, and, according 

 to this writer, the endosarc is a product of the mantle, originates the reproductive elements of the 

 colony, and possibly enters largely into the composition of the tentacular sheath. 



Such are the common attributes of a Moss-animal of the higher grade. In some forms, however, 

 the pharynx (Fig. 23, pk] is more developed than in others, and the alimentary canal is divided into a 



higher or cardiac (c, c), and a lower or pyloric cavity (/>). 

 A gizzard is occasionally present in both marine and 

 fresh-water forms, aiding the processes of digestion. 

 Primitive excretory organs are also developed in the 

 form of kidneys in some species. Many Bryozoa are 

 further characterised by the presence of a valvular 

 organ, the epistome, situated on that side (neural) of 

 the mouth nearest to the nerve centre. This singular 

 organ (Fig. 18, e) has been compared with the epi- 

 glottis of the throat of mammalian animals. It is 

 Fig. 22.-A, B, COMMUNICATION PLATES AND PORES IN moyed v i gorous iy up and down when the alimentary 



CELL WALLS OF MEMHRANIPOHA MEMBHANACEA ; C, J 1 



PERFORATED STEM OF zooiiOTRYON. (After Eeichert organs are partially protruded from their cells. Re- 

 and Nitzsche), garded by some as an organ of sense, it acts as a 



cp, Plates; p, Pores. . . . 



protection to the entrance of the gullet ywi), and its 



existence distinguishes the " gullekguarded " Moss-animals from those destitute of that structure ; 

 others, however, consider the epistome to be the equivalent of the foot of the mollusc, and there 

 is no doubt that it serves as an organ of locomotion in that abnormal " mouth-footed " genus, 

 Hhabdopleura, in which it retains its greatest development. (Fig. 18, A.) 



Peculiar organs termed ovicells occur periodically in many Bryozoa of the first rank, in the 

 form of external capsules or enlargements of the cell wall. They are often situated 

 at the upper part of the animal chamber over-reaching its orifice. (Fig. 24, B.) These 

 modified cells bud from the membranous walls of the cell and communicate with 

 the perivisceral cavity. As their name implies, the ovicells retain the fertilised ova, 

 which migrate into the pouch thus formed, and are finally liberated when fully 

 matured as active ciliated larvae. In a more complex form of ovicell the external 

 opening of this brood chamber is closed by a membranous capsule furnished 

 with muscles, by which it is withdrawn to facilitate the passage of the embryo 

 Moss-animal into the sea-water. Occasional enlargements of the cell wall, and cells 

 restricted to reproductive purposes, occur in some members of the inferior marine 



sub-orders. But the true ''brood-chamber" or marsupium appears only in the most -pj 2 3 ALIMEN 



highly organised sub-order of " lip -mouthed " Moss-animals (Cheilostomata),* which TARY CANAL OF 

 are further characterised by the presence of two kinds of movable appendicular 

 organs developed on the external covering of the colony, and irregularly dis- 

 tributed over its surface. The "vibracula}" consist of a long slender bristle, 

 thickest towards the base (Fig. 25, A, v), seated on a prominence in a hollow cup or receptacle the 

 representative of a cell containing only the muscles which direct its lashing movements. Mr. Busk 

 says : "These whip-like appendages serve as defensive and cleansing organs, and may be observed in 

 almost constant motion, sweeping slowly and carefully over the surface of the colony, and removing 

 whatever might be noxious to the delicate inhabitants of the cell when the tentacles are protruded." 

 In the family of Selenaridse, which are never attached to foreign objects, even when, adult, they are 

 enormously developed, and serve as organs of locomotion, by means of which Mr. Busk has observed 

 the colony to be transported from one locality to another. 



The second kind is that one form of which was first recognised and described by Ellis, in a 



* Greek, ckeilos, lip. 



ph 



CELLEPORA. (After 

 Hinclcs). 



c. c, Cnrdiap. p. Pylori p,. 

 cavity of Intestine. 



