284 University of California Publications in Zoology [Vol.19 



External Anatomy 



Margeana californiensis (fig. 1) is a small distome ranging in 

 length when alive from 2.4 to 5 mm. The smallest sexually mature 

 individual found had a length of 2.4 mm., and had large numbers of 

 eggs in the coils of the uterus. Several immature specimens were also 

 found, the smallest of which (fig. 5) had a length of 1.5 nun. Figure 

 1, which is a camera lucida drawing of a large-sized living specimen 

 of Margeana californiensis slightly compressed, gives an idea of the 

 size and shape. The body has considerable power of extension and 

 contraction, so that the dimensions vary in both living and preserved 

 specimens according to the degree of contraction. Measurements of 

 width and thickness were made from a series of sections. The thick- 

 ness of the body in the region in front of the testes was found in this 

 series to be about two-thirds of its width. Posteriorly the body was 

 somewhat flattened, having a thickness in the region back of the 

 testes of a little less than half of its width. In the series of sections 

 studied, in the region of the oesophagus the width was 0.56 mm. and 

 the thickness 0.36 mm. ; at the level of the ventral sucker the width 

 was 0.64 mm. and the thickness 0.38 mm. ; and half way between the 

 testes and the posterior end the width was 0.68 mm, and the thickness 

 0.23 mm. 



All the surface of the body except the posterior one-fifth is covered 

 with tiny scale-like spines set very closely together in rows encircling 

 the body. These spines are so small that they cannot be clearly dis- 

 cerned at the magnification of figure 1. Back of the testes the spines 

 begin to thin out, and in the larger specimens the posterior one-fifth 

 of the body is entirely smooth. In the smallest immature specimen 

 studied, however, the body was completely covered with spines. This 

 suggests that the thinning out of the spines in the posterior part of 

 the body of this species is due to the very great proportional growth 

 of the postacetabular region. 



The oral sucker has a slightly greater width than length, and 

 in a living specimen 5 mm. in length had a diameter of 0.4 mm. The 

 ventral sucker in this same individual had a diameter of 0.25 mm. 

 The measurements of the suckers of seven toto mounts of specimens 

 killed by Looss' shaking method is shown in the following table. 



