xvn ANATOMY BROWN BODIES 4/1 



as in Fig. 234. The ectocyst is prolonged through the orifice 

 (o) as far as the diaphragm (rf). 



Forms with a calcareous ectocyst are commonly ornamented 

 with ridges or other patterns, which are often of great beauty. 

 The ectocyst in these cases is commonly interrupted at intervals 

 by pores (Fig. 239, C), into which processes of the " endocyst " 

 the living, internal part of the body-wall extend. These may 

 appear as superficial pores, which apparently open to the exterior 

 in the dried condition, or they may perforate the septa between 

 adjacent individuals. This may be strikingly demonstrated by 

 decalcifying a branch of Crisia (Fig. 237), in which the zooecia 

 then appear connected by numerous strands of tissue. In many 

 marine forms the communications between the individuals are in 

 the form of small sieve-like plates known as " rosette-plates." 



The endocyst may consist of definite layers of ectoderm (em) 

 and mesoderm (mm), as in Fig. 234, but the mesoderm is 

 commonly in the form of a loose network, some of which is 

 attached to the body-wall, some to the alimentary canal, some 

 forming connecting strands between these two layers, and other 

 cells floating about freely in the body-cavity. These mesodermic 

 structures are often spoken of as the " funicular tissue," since one 

 or more strands of it commonly take on the form of a definite 

 " funiculus " (/). This structure may bear the ovary (or), while 

 the testes () are found, commonly in the same zooecium, attached 

 to various parts of the body-wall. The eggs and spermatozoa, 

 when ripe, break off and float freely in the body-cavity. 



The funicular tissue was at one time described as a " colonial 

 nervous system." The idea expressed by this term must be 

 considered erroneous from the fact that no nervous co-ordination 

 of the individuals is known to exist, in the vast majority of 

 cases. The actual nervous system consists of a ganglion (#) placed 

 between the mouth and anus of each polypide, and lying in a 

 small circular canal (not shown in Fig. 234) which immediately 

 surrounds the oesophagus. This canal is developed in the bud as 

 a part of the body-cavity, from which it becomes completely separ- 

 ated in marine forms. The Polyzoa have no vascular system. 



Brown Bodies. In the majority of cases, an extraordinary 

 process of regeneration takes place periodically during the life 

 of each zooecium. The tentacles, alimentary canal, and nervous 

 system break down, and the tentacles cease to be capable of being 



