r}32 Miscel/aneuiis. 



clGi'm, while the ciliated cells lose their cilia and travel into the 

 interior of the body, to take part iu the histogeny of the internal 

 organs. 



In Spongilla there are no strange elements between the ciliated 

 cells ; the processes nevertheless take place as iu Esperella. Beneath 

 the ciliated cells there lies a discontinuous layer of large rounded 

 cells, which, after the fixture of the larva, travel to the exterior and 

 form the permanent ectoderm. The only difference between K-^iier- 

 ella and SpoiKjiUa is that in the latter the true ectoderm is entirely 

 internal, separated from the outside b}' a continuous layer of ciliated 

 cells. 



2. Capture of the Ciliated Cells. — What happens to the ciliatc^d 

 cells in the interior ? A phenomenon here takes place which is 

 extremely singular and without parallel in the known processes of 

 embryogeny. 



The central nucleus of the larva is formed in greater part of large 

 cells, easy to i-ecognize owing to their large and perfectly round 

 nucleus, provided with a fine nucleolus, and in consequence of their 

 frequently containing vacuoles and a few coarse granulatioiis. 

 These cells in the free-swimming larva have a regularly rounded 

 outline. After the larva becomes fixed the ciliated cells, having 

 lost their cilia, shrunk, and become round, occupy a peripheral zone 

 immediately imderlying the ectoderm, which now comes into exist- 

 ence. The large cells in the interior become amoeboid and protrude 

 towards the former ciliated cells large and very active pseudopodia, 

 which capture them one by one. As soon as a cell is captured, the 

 contracting pseudopodium incorporates it, and the large cell regains 

 its rounded outline at this point, while in other dii'ections other 

 pseudopodia arise to continue the chase. 



These phenomena take place rapidly. Usually the capture is 

 completed in half an hour or an hour. The larva then rests for 

 about twenty-four hours without change. It appears spread out, 

 encircled by a fine extension-membrane, and completely crammed 

 with the large cells, which, now that they are in repose, are 

 ]icrfectly round, and exhibit around their proper nucleus, which lies 

 in the centre, a large number of little nuclei, the origin of which 

 wc have just seen. It is these nuclei which were taken by Goette 

 and ilaas for vitelline granules. I have always observed, contrary 

 to the assertions of the latter author, that they stain red in solutions 

 of carmine with an affinity for nuclei, and that Lyons blue respects 

 them so far as to substitute itself for the carmine in the nucleolus 

 belonging to the large cell before staining these supposed vitelline 

 granules. Methylene green also stains them more decjily than the 

 central nucleus. 



3. Formation of the AmpuUce. — After an interval of from twenty- 

 four to thirty-six lioui-s the captured cells begin to become active. 

 They increase in size, travel gradually towards the periphery of the 

 large cell, and finally emerge from it and become free again. Some 

 arrange themselves as a lining-membrane for the canals, while the 

 rest become grouped in hollow spherical masses and acquire first a 

 flagellum and then a collar lor the formation of the ampullie. The 



