] 12 Dr. M. Schultzc on the Development 



All Annelidan larvse, however, cannot be referred to these 

 divisions. For instance, the young of Sacconereis, as already 

 mentioned, possess several (four) bands of cilia at equal distances 

 on the body. The same is the case with a larva from Trieste, 

 described by J. MuUer (Monatsber. der Bcrl. Akad. 1851, p. 471) ; 

 it measured j^'", and possessed no bristles, but was distinguished 

 by the presence of bacillar corpuscles, like those in the skin of 

 the Turbellaria ; and also with the larva from Trieste with 2 strong 

 and 10-14 weaker circles of cilia, figured by Busch, tab. 9. 

 figs. 9 and 10, which was traced further by Max Miiller (Diss. 

 Inaug. Berol. 1852, p. 25, tab. 3. figs. 14-17), but without 

 arriving at its definite form. These young Annelida may be 

 denominated Poly trochee, after J. Miiller. 



Lastly, the general coating of cilia, which fi-equently occurs 

 in the earliest period of embryonic life [Chcetopterus, Sacconereis, 

 Nerei^ diversicolor) , but generally gives place to the isolated 

 circles, appears to be persistent in the same form throughout the 

 whole larval existence of many Annelidcs. For such J. Miiller 

 proposed the name of AtrochcB; he observed one of them at 

 Trieste, measuring j^^'", which was already furnished with de- 

 veloped setse (Monatsber. 1851, p. 472). 



All the young Annelides referred to these four divisions agree 

 in their development from the egg in the form of globular or 

 oval, non-annulated embryos, in receiving indications of division 

 into segments from the circlets of cilia when these are present, 

 but only acquiring the form of an Annelide, with distinct body- 

 segments and lateral bristles, after the lapse of some time. A 

 considerable deviation from this plan of development is presented 

 by Cystonereis Edwardsii, and Exogene Oerstedii and cirrata, 

 described by Kolliker, as also by Exogene naidina according to 

 Oersted, and Amphicora sabella according to 0. Schmidt. The 

 young of these animals acquire, whilst still in the fi^^, a form 

 similar to that of the mother, as they appear at their first forma- 

 tion divided into several segments, like the embryos of the Arti- 

 culata. In the embryos of Cystonereis Edwardsii, Kolliker 

 counted 8-9 segments, and 6 in Exogene cirrata. In these there 

 are no traces of circles of cilia, and even a general coat of cilia is 

 wanting ; whilst, on the other hand, fine cilia occur on certain 

 regions of the body, as in the embryo of Exogene cirrata on the 

 ventral surface. In these animals, therefore, we cannot speak 

 of a larval state, as they pass through all those changes of form 

 whilst still in the q^^, which gradually occur in the others during 

 their free- swimming period, and long after their embryonal ex- 

 istence. They are therefore destitute of the provisional, transitory 

 organs which characterize the larval condition of the others. 



To this short summary of the ])resent state of our knowledge 



