Miscellaneous. 73 



Kg. 2. Transverse section of a young form of Bhodophyllum. Lower 

 Carboniferous, Brockley, near Lesmahagow. 



Fig. 3. Rhodophyllum, sp., longitudinal section, showing the densely vesi- 

 cular character of the central area ; 3 a, transverse section of the 

 same. Lower Carboniferous, Langside, near Beith, Ayrshire. 



Plate III. 



Figs. 1-7. Transverse and longitudinal sections of a group of forms trans- 

 itional between Hhodophylhan and Aspidophylliim. Lower 

 Carboniferous, Brockley, near Lesmahagow ; Thirdpart and 

 Langside Quarries, near Beith, Ayrshire. 



MISCELLANEOUS. 



On the Embryology of the Nemertiaa. By M. J. Baerois. 



I HAVE already disputed the .line of demarcation hitherto established 

 between the two kinds of development of the Nemertina (development 

 by the differentiation oiallorula, and development by the coalescence 

 of four diseoidal plates) ; I have shown that the four suckers of 

 Miiller were not, as has always been supposed, peculiar to the Pili- 

 dium, but that they occurred in tyjjes hitherto regarded, as originating 

 from the direct differentiation of the Morula. 



Soon afterwards I succeeded in discovering the true signification 

 of the four suckers ; I found that the two anterior suckers constitute 

 the cephalic muscular masses, and the two posterior the delicate laminae 

 fohich form the ivall of the body. 



This statement is exceedingly important ; for we find in the deve- 

 lopment of all the Nemertians, even of those in which the develop- 

 ment is most simple, a stage in which there is a clear division into 

 two cavities, round each of which the various parts just mentioned 

 are formed, between the two the lateral organs and the oesophagus ; 

 round the first the cephalic masses, and round the second the laminse 

 of the wall of the body. In the Enopla this division into two cavities is, 

 from the first,very distinct. It is in the Anopla with a simpler deve- 

 lopment, such as Cephalothriv, that the matter is mostdifiicult of recog- 

 nition. In consequence of a peculiarity of structure belonging to this 

 group, the two cavities appear in it, from the first, united into a single 

 one ; nevertheless it is not difficult, especially after the differentiation 

 of the two great divisions of the musculature, to recognize without 

 hesitation their distinct existence. 



The constant and universal occurrence of this important stage, 

 whatever the group may be, enables us easily, starting from this 

 common point, to trace the divergences which give rise to the two 

 great divisions of the Anopla and the Enopla. 



Two phenomena are necessary to form one of the Anopla : — 1. The 

 lateral organs detach themselves from the oesophagus, and the pro- 



