Mr. H. J. Carter on the Re^yroduction of Sponges. 419 



on tlie stem of HalicJiondria ventilabrum : also a figure of T. 

 cranium growing in the bottom of the cavity of a specimen of 

 Halichondria ventilabrum^ from another jar in the British 

 Museum, labelled " Halichondria ventilabrum. J. S. Bower- 

 bank, 52. 3. 12. 54." 



The reader will at once observe that these are mere outlines 

 of the objects they are intended to represent, and not finished 

 drawings, as the latter would occupy more time than I feel 

 disposed to give them, and are not absolutely necessary for 

 the purpose, since, with the description and these diagram- 

 matic sketches, the general appearance of both species, with 

 their distinguishing characters, can at once be seen and 

 applied. 



In the illustration of T. cranium maybe observed a distinct 

 group of vents (fig. 9, a), to which attention is here directed 

 because Dr. Bowerbank in his diagnosis inserts, " Oscula and 

 pores inconspicuous " {ojj. cit. p. 83). But the distinctness of 

 the Avhorls or spiral lines of spicules (fig. 9, bb) must be viewed 

 as diagrammatic, since in the natural state they no more ap- 

 pear than in the hair of the human crown. 



I have also added a group of the bihamates magnified 

 (fig. 9, c) , which are not to be found in T. zetlandica. 



The word ^' bihamate," first applied by Dr. Bowerbank' to 

 this spicule, does not always meet the requirements of the 

 case, although it is quite as good as any other that has been 

 chosen. The name, however, does not matter, so long as we 

 remember that it is a C- or S-shaped body, of a more or less 

 spiral tendency, with the ends so turned in opposite directions 

 that, if laid on a flat surface, they do not both rest on the same 

 plane ; so that, in whatever position the bihamate is, one end 

 is always projecting, ready to catch any thing that may come 

 into contact witli it : hence Dr. Bowerbank has placed this form 

 among his "retentive spicula" of the sarcode. 



Nature, however, does not always require them for this 

 purpose, as they are absent in T. antarctica and T. zetlandica^ 

 where the sarcode is held together apparently without any 

 thing else of the kind. The habit of assigning a cause for 

 every thing that Nature does more frequently meets with con- 

 tempt than admiration. 



Reproductive Process. 



As with Tetliya cranium^ so with T. zetlandica ] both species, 

 in the adult condition, are richly charged with the small 

 globular and compressed elliptical bodies (fig. 13, ddd) first 

 described and figured by Johnston under the designation of 

 " oviform " {pp. cit. p. 84, pi. 1. fig. 8). Those in T. cranium 



