566 THE ANATOMY OF INVERTEBRATED ANIMALS. 



undergoing retrogressive metaniorphosis, is cast out of the 

 body. 



From these facts, and from the circumstance that the en- 

 do^^lastules of Infusoria, which are merely dividing, acquire 

 the striated structure, it must be conchided that the ascrip- 

 tion of a spermatozoal nature to the striae of the modified en- 

 doplastules is not warranted. And the remarkable observa- 

 tions of Biitschli, Strassburger,' Van Beneden, and Hertwig,^ 

 on the changes which take place in the nuclei of both animal 

 and vegetable cells, which are undergoing division, or are pre- 

 paring for fecundation, seem to leave no doubt as to the jus- 

 tice of this negative conclusion. In such cells the nucleus 

 becomes elongated and assumes a striated appearance, so as 

 to resemble in a very striking manner the so-called " seminal 

 capsule " of the Infusoria. Nevertheless, it is still possible 

 that the conjugation of the hifusoria may be a true sexual 

 process ; and that a portion of the divided endoplastules of 

 each may play the part of the spermatic corpuscle ; the con- 

 jugation of which with the nucleus of the ovum appears, from 

 recent researches, to constitute the essence of the act of im- 

 pregnation. 



With the proof that the " acinetiform embryos " of the 

 Infusoria ciliata are parasites, the view of the relations of 

 the Tentaculifera with the Ciliata, suggested at p. 101, 

 ceases to be exactly tenable. Nevertheless, the resemblance 

 of the ciliated young Acinetm to the simpler forms of the 

 Ciliata is so close that they may still be said to be modifi- 

 cations of a common type. Hertwig ^ has made the interest- 

 ing observation that, in some Acinetop, the tentacula are of 

 two kinds : those of the one kind are the characteristic suc- 

 torial organs, while those of the other kind are simply pre- 

 hensile, and have a structure very similar to that of the pre- 

 hensile pseudopodia of the Actinopliryidm. The same au- 

 thor shows that the ciliated germs do not arise from the en- 

 doplast alone, but that a portion of the protoplasm of the 

 body invests each division of the endoplast. In fact, the pro- 

 cess by which these germs are developed is altogether similar 

 to ordinary cell-division. 



1 " Ueber Zellbildung und ZcUtheilung," 1876. 



2"Beitriisre zur Kenntniss mid Bilduncr. Befruchtung und Theilung des 

 thierischen Eies." (" Morphologisches Jahroueh," 1876.) 



8 " Ueber Podnphrya gemmijmra nebst Bemerkungen zum Bau und zur sy- 

 stematischen Stellung der Acineten." (" Morphologisches Jahrbuch," 1876.) 



