ACANTHOCEPHALI 253 



processes the different parts of the " embryonic nucleus " 

 have also enlarged considerably, and thus have once more 

 approached somewhat nearer to the larva in size (Fig. 114 

 B). At the same time the differentiation and development 

 of the different organs begin. 



From the preceding description, which contains the chief 

 features of Leuckart's discoveries, it is seen that the 

 largest part of the worm arises from that frequently men- 

 tioned central mass into which the nuclei are said to retreat 

 at the beginning of development. The more recent state- 

 ments of Kaiskr also agree in general with this conclusion. 

 Since it appears that, owing to improved methods, certain 

 processes have been more elaborately worked out by him, 

 and since these are of a most peculiar nature, his obser- 

 vations will be considered here more at length, although it 

 is difficult to obtain a clear idea of the complicated processes 

 from his brief communication, unaccompanied as it is by 

 illustrations.^ 



After the larva of Echinorhynchus gigas has attached itself to the 

 wall of the intestine, and the middle part of its body has become greatly 

 swollen, groups of cells are said to detach themselves one after the other, 

 to become surrounded with cytoplasm, and thus to form the cells which 

 produce the permanent hooks of the proboscis. The groups of cells 

 move forward and finally unite to form the proboscis, which at length 

 can be everted. At about the same time the permanent body-covering 

 of the worm is formed by the detachment of nuclei from the entire 

 periphery of the "embryonic nucleus" and their migration into the 

 outer layer of the body plasma (Fig. 114). Accompanying an active 

 division of the nuclei, there is soon formed a very regular body-epithe- 

 lium. Here also the cuticula of the larva appears to be cast off, just as 

 its provisional hooks are. The epithelium secretes a new cuticula, and 

 beneath it a colourless, tenacious product, the fibrous tissue of the so- 

 called subcuticula. The muscular elements which are found in the sub- 

 cuticula are said to be formed at the same time from the cells of the 



^ [A paper by Hamann (Appendix to Literature on Acanthocephali) and 

 especially a voluminous work by Kaiser have furnished us with a new 

 exposition of the development of Echinorhynchus. These investigations 

 elucidate to a great extent the remarkable developmental processes, which 

 are here only briefly touched upon. We refer to these two works them- 

 selves, since it is not possible to give in this place the results of these 

 extensive studies. — K.] 



