The life history of Diplodisciis temporatus Stafford. 647 



interlace and anastomose. Between the branches many small cavi- 

 ties are left, which in the livins;- worm are filled with fluids. 



The body musculature. 



The only observations I have been able to make on the develop- 

 ment of the muscles are as follow^s: in young- cercariae, when the 

 other organs were clearly marked out, it was noticeable that some 

 of the cells lying- just beneath the investing- membrane became 

 diiferentiated from the surrounding cells b}^ a characteristic appearence. 

 The nuclei w^ere arranged on the inner side of a mass of cytoplasm 

 in which there appeared fibrillae, which Avere most noticeable in 

 longitudinal sections. In none of my material could I trace the 

 later stages in the transformation, nor, indeed, in the fully developed 

 cercariae did I succeed in demonstrating- the muscular structures 

 which have been described by Bettendorf (1897). 



3. The development of the tail of the ce r caria. 



In early stages of the development of the cercaria, when it be- 

 comes elongated and the anterior end is recognisable through the 

 formation of the primordium of the anterior sucking disc, the poste- 

 rior end becomes considerably narrowed. This narrow portion con- 

 tinues to elongate as the embryo increases in size, until it eventu- 

 ally becomes about three fourths the length of the body. When first 

 clearly distinguishable, the tail consists entirely of a mass of 

 meristem cells. In its later development, there is a special differen- 

 tation in three regions. Some of the cells near the surface become 

 differentiated into epidermal cells and secrete a cuticula similar to 

 that which covers the body of the cercaria. Just internal to the 

 basement membrane (investing membrane) there is developed a thin 

 layer of longitudinal muscles. At the centre of the tail there is 

 a central axis of muscle fibres, w^hich is at many points connected 

 with the muscular layer beneath the basement membrane. The bulk 

 of the tail is made up of a mass of parenchyma cells which resemble 

 the large vacuolated cells (Blasenzellen) which are developed in the 

 ventral part of the body of the embryo. The tail is at first a 

 direct continuation of the body of the embryo. In later stages of 

 development it becomes separated from the body by a cutinized 

 wall, except along the edges where it is connected by a number of 

 muscular fibres, the so-called '"connecting strands". 



