vitelline ducts. Very often .separate vitelline cells return to the vitelline 

 ducts with the contractions of the uterus. After a certain period the eggs 

 close, and at the place of the opening remains a little foot of the egg which 

 lies behind the uterus at the place of junction of the vitelline ducts. In such 

 a fashion, as much as can be ascertained by these intermittent observa- 

 tions, the little foot of the eggs of Dactylogyrus appears not as an individual 

 specially formed outgrowth but corresponds to the wall of the egg pressed and 

 elongated like the "little nose" of an electric bulb," (Bychowsky, 1933). 

 Views similar to the one described were observed in a number of other 

 monogenetic trematodes, fresh water as well as marine. However, there 

 is still much that is not clear. In the beginning, in the ootype the shell of 

 the eggs, as is obvious from the preceding, has a soft consistency and only 

 after a certain time hardens. This was noticed earlier by a number of re- 

 searchers. Thus, Kulwiec (Kulwiec, 1927) writes that the egg of Dactylogyrus 

 anchoratus (Dujardin) in the ootype (uterus by her terminology) is soft and 

 during the contractions of the body changes its shape. 



There are different opinions concerning the formation of the egg 

 shell. Some authors (predominantly of the last century) think that it is 

 formed at the expense of glands which are now designated as Mehlis gland 

 and formerly called shell, and others that the shell is formed at the expense 

 of the "shell" secretion of vitelline cells and that the secretion of the "shell" 

 glands is of no, or in extreme cases, of very little significance in this pro- p. 88 

 cess. The last point of view, substantiated by certain histological studies, 

 appears to be more or less generally recognized at the present time. It 

 appears to us, however, that this question cannot be considered as finally 

 settled. First of all, there are no sufficient basest) maintain that the egg 

 shell and its derivatives, that is the little foot and filament (see further 

 page 90 ), are fully and always homologous. If this (explanation, nobis) is 

 quite possible for eggs with a small foot and filament, on the other hand, it 

 is easier settled negatively for the eggs with comnlex and strongly developed 

 derivatives. Thus in the sections through fully formed eggs of Acanthocotyle 

 verilli Goto, we see (Fig. 112) that the envelope of the egg is colored some- 

 what differently than the posterior part of the little feet which apparently 

 are formed at the expense of a different secretion than the envelope itself. 

 In the formation of eggs of Diplectanum aculeatum Parona and Perugia, one 

 can likewise observe that this process is sufficiently complex. The uterus 

 is filled with a liquid which is possibly produced by the shell glands even 

 before the formation of the egg. At first, the egg cell gets into the uterus 

 and then the vitelline cells. The vitelline cells enter the uterus by portions 

 and immediately after they appear in the narrowed first part of the uterus, 

 the egg shell begins to form. After the cessation of the influx of the vite- 

 lline cells and the formation of the shell , at the posterior end of the latter 

 there remains an opening into which several vitelline cells pass back into 

 the narrowed anterior part of the uterus. At this time around the cells 

 which have come out, a little foot begins to grow further and further from 

 the end of the egg in the shape of a hollow little pipe. Then the moment 



87 



