Bekde.J Carboniferous Invertebrates. 11 



their skeletons make solid strata of limestone several feet in 

 thickness, extending over vast areas. Under such conditions 

 we always find a single species appearing in many forms, and 

 consequently great care should be taken in separating them into 

 species and varieties. So far as the external form and appear- 

 ance of the Kansas Fusulinas are concerned, I think it will be 

 impossible to divide the species, though a more careful study 

 of the minute structure of the interior of large numbers of in- 

 dividuals may reveal certain constant variations worthy of va- 

 rietal or even specific recognition. But even then, when the 

 fact is taken into account that they are but simple undifferen- 

 tiated animals, susceptible of such great variations from environ- 

 ment, great care would have to be taken in not making too 

 many divisions of them. 



Say's description of Miliplites secalicus is good enough, when 

 the locality from which his specimens were taken is brought 

 into account, so that it is practically impossible for it to be 

 missapplied, and consequently that specific term, together with 

 Fischer's generic designation, will stand. 



SPONGIiE. 



The sponge is a rather loose collection of single cells variously 

 grouped into one mass, forming a compound organism. The 

 connection of the different cells with each other is slight. These 

 cells are arranged in a series, so that canals are formed running 

 through the sponge, the cells facing the canals. The inner ca- 

 nals are generally larger where they flow together for the water 

 to flow out, and this enlargement is called a " cloaca." Water is 

 kept flowing through the canals by means of rapidly moving 

 cilia which some of the cells possess. These little whips also 

 aid in the capture of particles of food, which are taken from the 

 water as it flows through the canals. 



The cells of the sponge are held together by horny, calcareous 

 or flinty needles called spicules. The sponge of commerce, as 

 we generally see it, is not the entire animal, but only its skele- 

 ton, made up of horny fibers so interlaced as to form a network. 



