Skeleton in the Anomocladina. 237 



Sponges established by Zittel*, were originally defined by 

 him as distinguished by their " unregelmassig astige Skelet- 

 korperchen deren Aeste in einem knotig verdickten Centrum 

 zusammenstossen. Da dieselben an ihren Enden nur massig 

 verzweigt sind, so entsteht ein mascliiges Netzwerk, das in 

 nianchen Fallen grosse Aelinlichkeit mit dem Gittergeriist 

 gewisser Hexactinelliden erhalt," &c. 



Oscar Schmidt f subsequently described an existing repre- 

 sentative of this group, previously only known in a fossil state, 

 and confirmed and extended Zittel's observations. He recog- 

 nized the branched corpuscles and two kinds of nodes in the 

 network which they form by their union, one kind provided 

 by the centrum of the corpuscle, the other formed by the union 

 of the ends of its rays with those of adjoining corpuscles. 



Quite recently Zittel J, being unable to find more than one 

 kind of node in the network, and that formed by a union of 

 the ends of the rods, concludes that he was mistaken in sup- 

 posing that the corpuscles consisted of a centrum and radiating 

 arms, and proposes an amended definition of the Anomocla- 

 dina, as follows : — " Skeletal elements consisting of simple, 

 generally straight, but sometimes curved rods, more or less 

 strongly branched at the two extremities. The branched ends 

 of several (4-9) neighbouring rods meet together, and by 

 their amalgamation form the nodes." 



By the method which I find most successful in studying 

 Lithistid skeletons (boiling in caustic potash) it is easy to 

 completely isolate the corpuscles of Vetulina, and they are 

 then found to exhibit the characters which Zittel first assigned 

 to the corpuscles of the Anomocladina, and which were sub- 

 sequently seen by Schmidt. Further, by my method of 

 cutting frozen sections § it is possible to obtain a layer of the 

 skeletal network only one corpuscle thick (less if needful), and 

 then one clearly perceives that there is, as a rule, but one kind 

 of node, only this is not produced by the union of the ends of 

 the corpuscular rays, but by the centrum of the corpuscles, 

 against which the rays of neighbouring corpuscles abut. About 

 the place of abutment the centrum throws out numerous 

 branched spines, which, except in successful sections, make 

 interpretation of the structure difficult. In some cases the 



* Zittel, ' Studien liber fossile Spongien,' ii. Abth., Lithistidae, 1878, 

 p. 23. 



t O. Schmidt, ' Die Spongien des Meerbusen von Mexico,' 1879, 

 p. 29. 



X Zittel, " Ueber Astylospongidae und Anomocladina,'" JB. Mineral. 

 1884, ii. p. 75. Translated by W. S. Dallas, < Annals ' (5), xiv. p. 271. 



§ Sollas, " An Improvement in the Method of Using the Freezing 

 Microtome," Quart. Jouru. Micr. Sci. n. s. xxiv. p. 16.3. 



Ann. & Mag. N. Hint. Ser. 5. Vol. xv. 17 



