266 A MOXOGEAPn OF THE AUSTRALIAN APHRODITEA, 



or oval cells witli a delicate but distinct cell-membrane and 

 golden-yellow, oil-like contents, with, a nucleus, or, more 

 frequently, two or three. It seems very likely that there is a 

 delicate cuticle lining this layer of cells internally, but I hav^ 

 not been able to demonstrate it ; it must be very delicate, as a 

 very slight pressure is sometimes sufficient to cause the yellow 

 cells to break loose into the cavity of the ccccum, and pass along 

 into the intestine. 



Among these yellow cells are a number of cells (pi. vi., fig. 2.) 

 of about the same size, but of a very different character. Each 

 consists of a delicate, transparent cell-wall, enclosing a varjdng 

 number of smaller cells, each of which again consists of a delicate 

 transparent sac enclosing a spherical green body, which varies 

 in size in diiferent cells, but is always considerably smaller than 

 the enclosing sac, leaving around it a transparent space. The 

 central green corpuscle appears hom.ogeneous, and may be of an 

 oily nature. The nature of these cells remains somewhat doubtful ; 

 but they are most probably early stages in the development of 

 the yellow cells. They usually occur distributed pretty regularly 

 among the yellow cells, so as to produce an appearance of dark 

 mottling in the otherwise yellow ca3ca. More rarely they are so 

 numerous as to give the whole crccum a dark appearance. 



The principal functions of dorsal portion of the cpoca are 

 undoubtedly secretory ; they are to all intents and purposes 

 secreting glands, never being found to contain food-particles. 

 The secretion consists of the contents of the j-ellow cells, and is 

 driven out by the action of the cilia and by the peristaltic con- 

 tractions to which the croca are subject. The ventral portions 

 of the cceca are most probably the principal seat of the digestive 

 and absorptive processes ; the tube of the intestine itself is seldom 

 found to contain food iu specimens that have been kept for a 

 short time in clean water. 



