18 * Mr. H. M. Bernard on 



with all his ingenuity, has to make frames for constructing 

 arches and circular buildings, and moulds for circular casts ; 

 his cement has to be brought from a distance and carefully 

 manufactured, and he requires good sight and much aid to 

 form his dwelling : whereas some of the most skilful and 

 beautiful formations of these marine annelids are executed by 

 creatures devoid of eyes and with a soft and delicate body, 

 whose mortar is secreted by the glands of their skins, and 

 whose inborn instinct enables them to dispense with all 

 artificial aids in the construction of their homes. 



II. — The Endostermte of Scorpio compared loith the Homo- 

 logous Structures in other Araclinida. By H. M. Bfenard, 

 M.A. Cantab, (from the Huxley Kesearch Laboratory, R. 

 Coll. of Science, South Kensington). 



[Plate m.] 



Special interest has attached to the endostemite of Scorpio 

 on account of its bearing upon the question of the relationship 

 between Scor2)io and certain near allies of Limulus. The 

 external likeness between Scorpio and SUmonia taken alone 

 might be merely a case of convergence ; but their common 

 possession of an endosternite seemed to many to establish 

 beyond doubt that this resemblance was due to a direct 

 relationship. The validity of this argument depends, how- 

 ever, upon it being shown that their respective endostemites 

 are morphological equivalents. Indeed, it seems to me that 

 the whole question of the assumed relationship depends upon 

 the settling of this point ; for it is hardly possible that two 

 forms so related should possess analogous structures of funda- 

 mental importance in the organism which are not also homo- 

 logous. 



Considering, then, the interest attaching to the endostemites 

 it is somewhat to be wondered at that no serious attempt * 

 has been made to obtain a clear idea of their essential mor- 

 phology in the only way this can be obtained, viz. by 

 comparison. 



The Arachnid which at the outset seemed to promise most 

 light on this subject was Galeodes^ in which the three posterior 

 cephalothoracic segments remain unfused. This primitive 

 feature could hardly fail to find some reflection in the structure 

 of the endosternite. 



* C/"., however, Laukesttr, •' i»u the .^koloto-trophic Tisaues of Zimjm/u.s, 

 Scorjiio, iiud Mi/i/aU'," Q. J. M. S. vol. xxiv., 1884. 



I 



