292 Dr. J. E. Gray on the jpeculiar Structure 



ceding table ; but I shall content myself with indicating the 

 following : — 



1. The analogous muscles in the hip-joint and shoulder- 

 joint of the same side of the body are arranged in reverse 

 order — thus confirming the opinion of Vicq d'Azyr that the 

 left leg should be compared with the right arm, and vice 

 versd. 



2. The marsupial muscles in no respect correspond with the 

 obturators, but find their true analogues in a muscle whose 

 direction lies between that of latissimus dorsi and the pectorals. 

 This muscle (wanting in the Alligator and Crocodile) is found 

 in the following animals : — -the Armadillo, the Seal, the Otter, 

 and other animals that dig or swim. 



3. The analogue of the obturators is found in the second 

 pectoral of the birds, which acts as a levator humeri, and 

 Avhose line of direction lies between the pectorals. This mus- 

 cle may possibly be represented in the Crocodile and Alligator 

 by the pectoral muscle extended from the first sternal rib to 

 the posterior edge of the coracoid. 



XXXVIII. — On the peculiar Structure and Function of the 

 Spicxdes of Hyalonema. By Dr. J. E. Geay, F.R.S., 

 V.P.Z.S., F.L.S., &c. 



One of the chief reasons assigned for regarding the rope-like 

 axis of Hyalonema as part of a Sponge, to which some speci- 

 mens have been found attached, is that it consists of spi- 

 cules which are composed of silica, and formed like the spi- 

 cules of sponges. Prof. Max Schultze, Prof. Wyville Thom- 

 son, and others compare them with the long filiform spicules 

 of Eivplectella. 



Zoologists and microscopists have overlooked the importance 

 of a very marked peculiarity in the formation of the spicules 

 of Hyalonema that is not to be observed in the spicules of any 

 kind of Sponge that I have examined or seen figured. This 

 is the more remarkable as the peculiarity to which I refer 

 was mentioned when I first described the genus, and is figured 

 by Max Schultze, Brandt, and Bocage, and, indeed, by all au- 

 thors who have figured the genus ; but these authors have not 

 considered why the peculiarity existed and the bearing it has 

 on the question of the structm-e of the animals to which the 

 spicules belong. 



The spicules of Sponges are formed of a number of con- 

 centric layers round a central line, and they always have a 

 perfect, more or less acute end, which is simple and formed of 



