IV 



PHYLUM CGELENTERATA 



231 



In the case of the female the segmentation appears to be equal from the 

 firsfc, and results in the formation of a blastula-like stage, which becomes 

 converted into a solid morula-like body by the passing inwards of a number of 

 cells. As in the male, the central cells multiply to form the sexual cells, and 

 the outer cells form the external layer with its segments. In all probability, 

 though this has not been actually proved, the mature sexual animals become 

 free from the plasmodia, and the females, after fertilisation, find their way to 

 another host where they are transformed into plasmodia, the germ-cells of 

 which are the fertilised ova. 



FIQ. 183. Saline 11 a, longitudinal section. (After Frenzel.) 



To be mentioned also in connection with the Dicyemidae and Orthonectidse, 

 as perhaps allied with them, are the remarkable parasites Am&bophrya and 

 Lohmanella the former living in certain Radiolarians (Protozoa), the latter in 

 the body-cavity of a F'ritillaria (Urochorda). These both resemble the groups 

 described above, and differ from the other Metazoa, in the presence of only a 

 single body-layer. This remarkable simplicity of body-structure occurs also 

 in Salinella, though too little is known with 

 regard to this animal to provide adequate data 

 for determining its affinities with certainty. 



Salinella (Figs. 183 and 184), which has 

 only been found in artificial saline solutions, 

 is a minute animal in the form of a somewhat 

 depressed cylinder, open at both ends, and 

 with a wall composed of a single layer of 

 cells. The anterior end is somewhat pointed ; 

 around the anterior opening or mouth, which 

 is ventrally directed, is a circlet of from fifteen 

 to twenty long whip-like cilia. The posterior 



aperture (anus), which is usually closed, is surrounded by a few stiff setae. 

 The ventral surface is flattened, and is covered with fine vibratile cilia, while 

 on the dorsal surface and the sides are regularly arranged rows of straight 

 " setae " (non-motile cilia). The internal cavity (enteron) is found to contain 

 sand, plant-fragments, and Bacteria ; its surface is beset with long cilia. 

 Multiplication is said to take place by transverse fission ; and a process of 

 conjugation followed by encystation has also been observed. 



Trichoplax and Treptoplax, which have been supposed to be Mesozoa, 

 appear to be merely special modifications of developmental phases of Hydrozoa. 



FIQ. 184. Salinella, transverse 

 section. (After Frenzel.) 



