P L Y Z O A 



167 



(Cristatella) having the form of a plano-convex ellipse and 

 locomotive (fig. 3). In addition to the multiplication 

 of polypides in a colony by budding, and to the annual 

 production of new individuals from fertilized eggs which 

 initiate new colonies, a reproduction by internal buds 

 called " statoblasts," comparable to tho gemmre of Spon- 

 gilla, has been observed in all the genera (fig. 3, I). The 

 statoblasts are developed from the funiculus (mesentery), 

 and are enclosed in ornate lenticular capsules of chitinous 

 substance, characteristic in form in each species. 



The fertilized egg of the Phylactolwma does not give 

 rise to a zonociliate larva, but to a uniformly ciliate cyst- 

 like diblastula, which develops directly and produces 

 polypides by budding. The Phylactolieuia are all inhabit- 

 ants of fresh water (lacustrine). 



Fio. 11. Semi-Weal view of paitof the lophophore of Lophopus and its tentacles, 

 intended to show the nerve-ganglion, nerves, and parts around the mouth. 

 The tentacles have been cut away all along the right arm of the lophophore and 

 from the inner margin of the left arm. c, foramen .placing the cavity of the 

 epistome in communication with the body-cavity; c', body-wall ; d, mouth; e, 

 the epistome or pra-oral lobe ; /, wall (if the pharynx ; A, wall of the intestine ; 

 t, anus ; k, lophophore ; I, a ciliated tentacle ; r, elevator muscle of the epistome; 

 IT, the nerve-ganglion ; x, x' t nerves to lophophore and tentacles y, nerve to 

 pharynx. 



The Phylactola?ma include the genera Lophopus, Cristatella, 

 Alcyonella, Plumatella, and Fredericella, which have been beauti- 

 fully figured and described in Allman's classical Freshwater Polyzoa, 

 Ray Society, 1856. The colonies of Lophopus are small, consist- 

 ing of half a dozen polypides embedded in a massive glass-like 

 ccencecium. Cristatella (fig. 3) is remarkable amongst all Polyzoa 

 for its locomotive zoarium. Alcyonella forms massive ccencecia of 

 many hundred polypides, as large as a man's fist. Plumatella and 

 Fredericella are delicate arborescent forms commonly encrusting 

 stones and the leaves of water-plants. All the genera known are 

 British. 



The Phylactolrema furnish a remarkable instance of a well- 

 marked zoological group being confined to fresh water. Their 

 reproduction by statoblasts (not known in the marine Polyzoa) 

 appears to be related to the special conditions of lacustrine life, 

 since it is also observed under the same exceptional conditions in 

 the single freshwater genus of another great group of animals, viz., 

 Spongilla. Also related to their non-marine conditions of life is 

 the development of the fertilized egg, which, as in so many similar 

 cases, does not produce the remarkable banded forms of locomotive 

 larvce which are characteristic of their marine congeners. 



Order 2. GYMNOL^EMA, Allman. 



Ectoproctous Eupolyzoa in which the polypide is devoid 

 any trace of the prre-oral lobe or epistome, whilst the 



lophophore is perfectly circular. The polypides of a colony 

 are frequently highly differentiated as avicularia, vibracu- 

 laria, ocecia (egg-receptacles), and even as root and stem 

 segments. The neighbouring polypides of a colony 

 communicate (?) with one another by " rosette-plates " or 

 " communication-plates " perforated areas in the walls of 

 contiguous zooecia. The greatest variety in the character 

 of the cuticle forming the zooecia (gelatinous, horny, 

 calcareous) and in the grouping of the polypides, as well as 

 in the shape of their zooecia, is observed in different 

 sub-orders and families. In addition to the ordinary 

 sexual reproduction, there are various modifications of the 

 process of budding, the full exposition of which would 

 necessitate more space than is here allotted, and is not 

 yet indeed within the possibilities of present knowledge. 

 The fertilized egg of the Gymnokema gives rise to 

 remarkable ciliate larvse of various 

 forms (figs. 19, 20, 21), from which 

 the first polypide of a colony is 

 developed l>y an extraordinary and 

 unexplained series of changes. 

 The Gymnola?ma are, with the 

 single exception of the genus Palu- 

 dicella, inhabitants of the sea. 



The Gynmolffima are divided, accord- 

 ing to the system of Busk, into three 

 sub-orders characterized by the shape 

 of their zocecia, and the nature of the 

 mouth-like margin which it presents 

 when the exsertile portion of the poly- 

 pide is withdrawn within it. The 

 Cyclostoma have long tubular zocecia, 

 often of large size and often calcified, 



laced side by side in cylindrical bun- 

 les, or in other definite grouping ; the 

 mouth of the zocecium is circular and 

 devoid of processes. There is little or 

 no differentiation of the polypides con- 

 stituting a colony. Host of this group 

 are fossil, and the living genera belong 

 mostly to southern seas. The genera 

 Crisia (fig. 13, A), Diastopora, Tubuli- 

 pora, and Hornera are typical. The 

 Ctenostoma have usually a soft zoce- 

 cium ; its orifice is closed by the folds 

 of the retracted polypide or by a 

 circlet of bristles which surround it. 

 Alcyonidium gdatinosum is the com- 

 monest representative of this group 

 on the British coasts. Bowerbankia 

 (fig. 1, A) and Paludicella (fig. 1, E) 

 also belong here. The ChSostoma 

 form the largest and most varied sub- 

 order of Gymnolfema. The zocecia are 

 horny or calcified ; their orifices can be 

 closed by a projecting lip in the form 

 of an operculum. The operculum is 

 a separable plate developed on the 

 cuticle of the retractile part of the 

 polypide, and lias muscles attached 

 to it (fig. 13, B, C, D). The surface 

 of the zooecia is frequently sculptured, 

 and its orifice provided with processes 

 and spines (fig. 1, C, F). Very usually 

 some of the polypides of a colony are 

 modified asavicularia,vibracularia, radi- 

 cal fibres, and ocecia. The avicularitnn 

 is a polypide reduced to a simple muscu- 

 lar apparatus workingupon the modified 

 operculum and zocecium so as to cause these hard parts to act as a 

 snapping apparatus comparable to a bird's head (fig. 12, o). They 

 are frequently found regularly distributed among the normal cells 

 of a colony, and probably have a cleansing function similar to that 

 attributed to the Pedicellaria?. of the Echinoderms. "Vibracularia" 

 are even more simplified polypides, being little more than motile 

 filaments, probably tactile in function. The opercula of zocecia, 

 ocecia, and avicularia have recently been used by Busk in character- 

 izing genera and species, in a systematic way. Stem-building and 

 root-forming polypides are frequently found, being closed pulvpidcs 

 which subserve anchoring or supporting functions for the benefit of 

 the whole colony. The stem of Kinetoskias (fig. 14) is produced 



Fio. 12. Two zooecia of Ata- 

 marchis (Bugula) avicularia, 

 Lmx. (Chiiostoma), of which 

 the anterior contains a living 

 polypide, whilst the posterior 

 is empty. To each is attached 

 one of the characteristical- 

 ly modified polypides known 

 as an " aviculaiinm" o\ the 

 hinder of these hiis grasped 

 and holds in its beak a small 

 worm. , anus; i, intestine; 

 t>, stomach ; r, body-cavity 

 (coelom) ; >, tentacular crown 

 surrounding the mouth ; te t 

 testis cells developed on the 

 surface of the terminal mesen- 

 tery or " funiculus " ; o, o, avi- 

 cularia. 



