FOSSIL BRYOZOA. 279 



The soft and perishable nature of the common dermal covering in the Ctenostomata and 

 Endoprocta would preclude their preservation in a fossil state. But it is highly probable that 

 these sub-orders also existed in past ages. For the structure and embryological history of the few 

 existing species belonging to those groups seem to indicate that they represent the earlier forms 

 of Bryozoonal life, when the primitive types were free when adult, as the ciliated larva is in the 

 first stages of development. Thus the fixed state and colonial growth may be regarded as modi- 

 fications occurring in the course of generations. The first kinds were probably solitary animals, the 

 first step towards colonisation being the development of that creeping tube, the stolon, which unites 

 the various shoots or cells into a colony of individuals, as in Pedicellina and the Ctenostomatous 

 forms. Thence all the varied colonial types may have differentiated, and all the organs for the 

 protection and common welfare of the colony were eventually developed. 



Differences in the form of the colony of parasitic species often result from the shape of the 

 organisms they infest, and singular modifications adapted for the life that is led are of frequent 

 occurrence. Thus, in a species of Membranipora which forms conspicuous white patches upon the 

 Gulf- weed, and other Algae, the skeleton is not universally hardened throughout. Certain parts 

 remain flexible and so escape fracture, when the thousands of united cells sway backwards and 

 forwards in the water, as the fronds of the weed are tossed to and fro by the waves. The shape of 

 the erect colonies depends chiefly upon the mode in which the budding takes place, and the situation 

 of the primary buds. In radiating and crust-like species, new cells often become interpolated. One of 

 the common Sea-mats grows so rapidly during the summer, according to Nitzsche, " that the edges 

 present a remarkable appearance. A marginal zone of perhaps one inch in breadth contains only 

 half-developed cells ; those nearest the centre, being least maturely calcified, are inhabited by smaller 

 polypides ; the younger ones are still uncalcified, and the cell orifice being as yet undeveloped, they 

 cannot protrude. Only a very small part of a marine colony contains completely developed 

 polypides. The younger cells at the extreme edge enclose immature buds, the older are empty, and 

 only those cells intermediate between the elder and the younger contain fully developed animals." 



Internal buds, called " Statoblasts," enclosing between two valve-like plates a polypide, which 

 remains in a quiescent state for a variable period, are also developed on the "funiculus," and liberated 

 as perfected Moss-animals, on the death of the parent. These are characteristic of the " gullet- 

 guarded " fresh- water genera, some of which also multiply by fission a form of budding in masses. 

 The life-history of the marine colonies, is likewise perpetuated by internal buds in each cell. The 

 chief features of this singular process, known as " the fall and renewal of the polypide," have been 

 minutely described by F. A. Smitt, but are still the subject of controversy. It appears certain, how- 

 ever, that on the dissolution of the polypide, a portion of the digestive organs separates from the rest, 

 and remains attached to the funiculus, a part of the endosarc, or common internal flesh of the colony. 

 This " brown body," or remnant, increases in size, at the expense of the fatty globules by which it is 

 surrounded, and is believed to give rise to a bud which develops into a perfect Moss-animal, resembles 

 its predecessor in the cell, and may profit by the perfections of the colonial system. For, strange to 

 say, the avicularian and vibracular appendages are not affected by the death of the animal inhabitant 

 of the cell on the outer wall of which they may be developed, their existence being independent of it, 

 and connected with the colonial system of which they are the outgrowths. 



Thus is the increase of the colony secured, and the life-vigour of its inhabitants renewed and 

 perpetuated. A word as to its original development. In most Moss-animals, both reproductive elements 

 are present in each cell. But there are a few exceptions to the general rule, as among some of the 

 Sea-scurfs, the Ctenostomata, and in the solitary Loxosoma, in which the sexes are stated to be dis- 

 tinct, the tufts of separated animals consisting either of male or female individuals. Sometimes the 

 ova, fertilised either before or after their expulsion in the water, are set free in the perivisceral cavity, 

 and escape only upon the rupture of the sac, and death of the parent polypide. Or they are dispersed 

 by means of special organs, or pass through the brood chamber, and a period of further development. 

 But in all cases they finally reach the water, as more or less developed, active, free-swimming larva?. 

 In this state they pass a variable period of time, swimming about by means of the cilia with which 

 they are clothed. Eye-spots are developed, and long bristles for touch and guidance. These are 

 absorbed when the little animal abandons its free life, becomes stationary, and develops into the 



