The life history of Diplodiscps temporalis Staffoed. 635 



stages of the embryo, after it has begun to elongate, fail to show 

 'any traces of these nuclei. 



Schwarze (1886), Tennent (1905) and others, have described 

 the origin of the investing membrane of the germ balls as taking- 

 place in the manner above described. 



Oetmann (1908), in describing the early germ balls in the 

 miracidium of Fasdola hepatica, says : "Bereits in diesem Stadium sah 

 ich den Keimballen eine Art Hüllzelle aufsitzend, die kapuzenartig 

 ihn überwölbte, wie ich dies schon oben bei Besprechung der Hüll- 

 membran angab (tab. 14, fig. 35 Kl^). Daß sie ein Elastomer des 

 Keimballens darstellt, scheint nach tab. 14, flg. 35, 36a, b, 37 sehr 

 wahrscheinlich. Wir finden eine oder zwei solcher kallottenförmiger 

 Zellen auch noch in weit spätem Stadien dem Keimballen aufsitzen, 

 ohne daß eine weitere Differenzierung an ihnen vorgegangen zu sein 

 scheint. Ihre Ausbildung zur Cuticula, wie sie Eüssbach beschreibt, 

 war nie zu beobachten. Offenbar findet sie noch nicht statt, solange 

 das Miracidium noch im Ei sich befindet oder freilebend ist, sondern 

 erst, wenn es in seinen ersten Wirt gelangt ist." 



His figures of these young germ balls (fig. 35, 36a, 36b and 37, 

 tab. 14), when compared with the germ balls represented inside the 

 body cavity of the miracidium (his fig. 38, tab. 14) show clearlj- 

 that in the cells (?) attached to these young embryos we have to do 

 with quite different structures from the investing cells of the older 

 embryos. The bodies attached to the two celled embryos (contrary 

 to all other recorded instances the cell outlines are less distinct in 

 the younger stages) contain no cytoplasm at all. They are clearly 

 shown as being made up of a small nucleus-like structure covered 

 by a thin membrane, so it seems hardly possible that from these alone 

 are to come the cytoplasmic membranes which will enclose the embryos. 

 In the light of my own observations on the formation of the 

 polar bodies of the parthenogenetic eggs of Biplodiscus, it would 

 seem most probable that the nuclei figured by Ortmann represent 

 polar bodies which are still attached to the segmenting eggs. The 

 structure of the attached nucleus in fig. 36b, lends suppord to this 

 view. In this figure the nucleus is represented as containing a 

 mass of chromatin which consists of rather fine granules scattered 

 irregularly through the interior of the nucleus, just as is the 

 appearance in early stages in the degeneration of a polar body. 



In the same paper the formation of the "'Hüllmembran" in 

 embryos from fertilized eggs is, on the other hand, described as taking 



