26 THE MICROSCOPE. Feb. 



These zooid.s are amueboid in tlieir nature. Both the 

 collar and liagellum can be inverted and be received 

 within the body of the animalcule. It can also send forth 

 processes, pseudopods, with or without the indrawing of 

 the collar and flagellum. 



Internal Structure. — In Keratose — horny — .sponges 

 the skeleton is familiar to all. The substance is named 

 " spongin." How Gelatinous sponges are held together, 

 may be inferred from what we observe in jelly fishes. 

 Calcareous and Silicious sponges, having possibly a more 

 fluid sarcode, are provided with spicules generally so 

 placed as to serve as a skeleton. These spicules are as 

 beautiful in form as multitudinous in variety. In some 

 species the spicules coalesce and cause thereby objects of 

 wondrous beauty as Venus flower basket {Ewplectella). In 

 others spicules are attached to the outside for defensive 

 purposes. 



In addition to spicules, and generally lying close to 

 them, sponges contain granular bodied irregular masses, 

 which have been recognized as amoeboid cells, and named 

 cytoblasts. Neither spicules nor cytoblasts come in con- 

 tact with the flagellate chamber. The exact functions of 

 these amoeboid bodies are as yet in doubt. As before 

 stated, it is believed that they exert whatever force a 

 sponge exercises. But it is further surmised that they 

 also take hold and remove all foreign substances which 

 have entered the sponge. In higher organisms other cells 

 and minute structures have been observed, the uses of 

 which have been difl'erently interpreted. 



Life History. — Of this little is known, much surmised. 

 Prof. W. J. Sollas of the University of Dublin, the 

 author of the article on sponges in the Encyc. Brit, quotes 

 authorities for the occurrence of both sexual elements in 

 the same individual, but in uneven quantities ; the male 

 predominating in one, the female in others. One author- 

 ity given by him found one male to 100 female forms. 



