26 NATURAL SCIENCE. Jan.. 



to be oviducts, and it has since been made evident that he did not 

 recognise the closure of the intestine in certain genera — a physiological 

 feature of ordinal value. But he divided the class into two orders, 

 so well differentiated by other characters, that the names of Lyopo- 

 mata (or loose valves) and Arthropomata (or jointed valves), which he 

 applied to them respectively, should retain priority over the Articulata 

 and Inarticulata, the Tretenterata and Clistenterata of other investigators, 

 of which subdivisions they are the exact equivalents. Owen's 

 researches on the internal structure of the Brachiopoda marked a 

 distinct advance in knowledge of this difficult and obscure group of 

 organisms. 



In a memoir on the anatomy of Clavagella, Professor Owen 

 noted the enormous development of the mantle in the " club shells" 

 as one of the instruments in the work of excavation for which these 

 bivalves are remarkable. Some observations on the camerated 

 structure in the valves of the water-clam [Spondylus varius) were first 

 printed in ihe Proceedings of the Zoological Society for 1837, when atten- 

 tion was directed to the chambered and septated condition of the 

 shell in that genus, and to the connection existing between the mode 

 of growth in Nautilus and that of other molluscs which partition off 

 a part of their shell not required for the convenience of the soft parts 

 of the animal inhabiting it. It was then distinctly stated that the 

 septal divisions of the Nautilus shell are analogous to the septa of the 

 *' water-spondylus," and many other shells which partition off" the 

 ■disused portion of their houses both among univalves and bivalves. 

 An investigation of the anatomy of the gasteropod family of the 

 " bonnet-shells" (Calyptreidae) proved of interest "as manifesting some 

 of the successive stages of complexity in the passage from the simple 

 Patella to the spiral valves." Professor Owen's studies of the uni- 

 valve mollusca in general, and of the recent Nautilus in particular, led 

 him to the conclusion that the Pteropoda had less affinities with the 

 Dibranchiate, or " two-gilled " cephalopoda, than the recent Nautilus. 

 This form he considered to be the type of an inferior order of tetra- 

 branchiate, or " four-gilled " cephalopoda, represented by numerous 

 fossil species, and as an osculant form between the cephalopoda and 

 gasteropoda. In consequence of this conviction, he transferred the 

 encephalous floating Pteropoda from above to below the Gastero- 

 poda's in his classification of the Mollusca, which is based chiefly on 

 the conditions of the respiratory organs, as a physiological character 

 intimately connected with activity of locomotive functions. 



The subject of the Pearly Nautilus had been strongly recom- 

 mended to his attention by Baron Cuvier, in whose dissecting rooms 

 young Owen enjoyed the privilege of working. The famous French 

 zoologist had never seen a specimen of the animal of this genus, 



13 The Pteropoda are now considered to belong to the inferior branch of the 

 class Cephalopoda by those who place the class Gasteropoda at the summit of the 

 Molluscan series. 



