THE AMERICAN 



MONTHLY 



MICROSCOPICAL JOURNAL 



Vol. V. 



Washington, D. C, March, 1884. 



No. 3. 



Fig. io. — Statoblast of 

 sponge. 



Serial Arrangement of Birotulate 



Spicules in Statoblasts of 



American Sponges. 



BY HENRY MILLS. 



The most common of the fresh- 

 water sponges is that known as Spon- 

 gilla Jiuviatilis^ Bk., Meyenia Jlu- 

 viatilis^ Carter. This species, in 

 some of its forms, 

 occurs in most of 

 our rivers and 

 ponds where the 

 conditions are 

 suitable to sponge 

 growth. The va- 

 rieties are numer- 

 ous in this coun- 

 try, and they difier 

 so widely from each other that it 

 might be less confusing to regard 

 some of them as distinct species. In 

 the course of my collecting tours last 

 summer and fall, I gathered many 

 specimens which, at first, presented 

 the appearance of one or other of the 

 varieties of this sponge which is de- 

 scribed and figured in its typical form 

 in. Bowerbank's Work on Sponges, 

 vol. I, plate xxii, fig. 319; also by 

 Carter in the Ann. and Mag. Nat. 

 History olY&hxwQxy., 1881. 



In the latter part of October, 1883, 

 while examining a specimen found 

 in Ischua creek, Franklinville, N. 

 Y., I was surprised at the peculiar 

 and well-rounded statoblasts, and re- 

 solved not to pass them by without 

 an effort to learn more about them. 

 For the purpose of a more critical 

 examination, I embedded a suitable 

 piece of the sponge in hot paraffin, 

 and cut thin sections of the statoblasts. 



afterwards mounting them in Canada 

 balsam. I was well rewarded for 

 my trouble, for to my surprise and 

 delight the wall of the statoblast in 

 section presented a serial arrange- 

 ment of the birotulate spicules, one 

 above another (fig. 10), which was 

 as beautiful as it was unique to me. 

 In these statoblasts the primary ro- 

 tules of the first series rest on the 

 chitinous coat ; the secondary rotules 

 of the same series extend about half 

 way through the wall. The second- 

 ary series, without resting on the 

 first, extends from about half way in 

 the wall to the outer crust and a little 

 beyond. In a few cases, however, I 

 have found three series of the birotu- 

 lates, the first and third arranged as 

 above, with a second intermediate. 

 The appearance of these statoblasts 

 in section is well shown in the figure, 

 in which it will be seen that the two 

 series of birotulate spicules are quite 

 regularly arranged about the central 

 cavity, forming a strong, resisting, 

 and protective envelope. The ap- 

 pearance under the microscope is 

 very beautiful, as the form of the 

 spicules is better seen than in the cut. 

 Whether this is constant, but to be 

 .seen only when thev sections have 

 been cut favorably for showing their 

 position, or whether it is casual and 

 abnormal, further observations are 

 necessary to determine. Without ac- 

 curate measurement I consider the 

 birotulates of each series to be alike. 

 The shafts are not spined, but are 

 almost cylinjdrical, having but little 

 of the hour-glass shape, as Mr. Car- 

 ter calls it, as distinguished from 

 those of the ordinary Meyenia Jluvi- 



