238 



lines Allopora and Distichopora , I have shewn that the ovum is sur- 

 rounded by a double layer of cells, the outer one being ectodermic 

 and the inner one endodermic in origin. Both of these layers are very 

 thin when the ovum is mature and it is not always a very easy matter 

 to demonstrate the existence of the two layers even when the speci- 

 mens are well preserved and the sections very thin. 



Although the history of the development of these gonophores 

 proves conclusively that both the ectoderm and endoderm enter into 

 their formation I have been anxious for some time to confirm the 

 existence of the two layers in other genera of the Stylasteridae. 



A little while ago, thanks to the kindness of Dr. Günther of 

 the British Museum, some specimens of ripe female Errina labiata 

 came into my hands, and I am able to demonstrate now the fact that 

 in this genus the ripe ovum is covered by layers of both ectoderm and 

 endoderm. Moseley was the first to describe the female gonophores 

 of Errina labiata and , altough his description is perfectly accurate in 

 every other respect , he apparently overlooked the inner endodermic 

 layer covering the ovum. »The ovum« he says »is covered over in the 

 cup by a reflection of the ectodermal investment of the spadix« and in 

 the figure he refers to, ectoderm and ectoderm only is drawn. 



The study of the female gonophore of Errina confirms , then, the 

 accuracy of the diagrammatic figure woodcut 7 that I have given in 

 my second paper on the gonophores of the Hydrocorallines (Q. J. M. 

 S. Vol. XXXII). 



5. Die Fortpflanzung von Planaria alpina (Dana). 



Von Dr. Walther Voigt, Bonn. 

 (Aus dem zoologischen und vergi, anatomischen Institut zu Bonn.) 



eingeg. 5, Mai 1892. 



In seinem Berichte über die zweite zoologische Excursion an die 

 Seen des Rhätikon [Verhandlungen der naturf. Gesellschaft in Basel, 

 IX, 1891, p. 477] äußert sich Zschokke über die Fortpflanzung der 

 Planaria alpina wie folgt : »Weder Kennel noch Egg er konnten je- 

 mals Eicocons der in Frage stehenden Turbellarie sehen, so daß 

 Kennel sich geradezu die Frage vorlegt, ob das Thier nicht viel- 

 leicht im Gegensatz zu seinen Verwandten vivipar sei. Dies scheint 

 mir nun ziemlich wahrscheinlich. Eier oder Eicocons bekam ich nie- 

 mals zu Gesicht, wohl aber zeigten sich im Glasgefäß, in dem alte 

 Planarien gehalten wurden , nach einiger Zeit ganz jugendliche 

 Thiere.« 



