The Microscope. 297 



appearance to the sponge. They may be straight or slightly curved, 

 smooth or spined, sharply or abruptly pointed. Second, the dermal 

 spicula; — these occur in the outer covering of the sponge, though 

 when mounted they are frequently dispersed through the whole 

 specimen. They are very much smaller than the skeleton-spicula 

 and are generally curved and spined, and may be sharp-pointed or 

 blunt-pointed. In more than one species the dermal spicula are 

 small birotulates. The third kind are the birotulates or two-wheeled 

 spicula of the statoblast, which are placed radially in its outer wall. 

 When there is only one kind of these the specimen is of the genus 

 Meyenia, so named from Meyen, who in 1839 first discovered these 

 bodies and their position in the statoblast. "When there are two 

 kinds of birotulates in the wall of the statoblast one longer than the 

 other the specimen belongs to the genus Heteromeyenia of Potts. 

 If the spicula lie horizontally or tangentially on or in the wall of the 

 statoblast the specimen belongs to the genus Spongilla of Carter. 



To enumerate all the spicula that occur in all the species would 

 extend this article beyond the proposed limits. The writer would 

 be glad to correspond with any who may find specimens. 



Buffalo, N. Y. 



A THOROUGHLY RELIABLE CEMENT. 



M. A. BOOTH. 



A TERSE, well-put sentence, appealing to a common experience, 

 -*• ^ often times has more weight than a page of labored logic. 

 And that member of the Postal Club who has so amusingly epito- 

 mized white zinc as 



" Glossy and white, 

 Cracked and broken. 

 Endorsed by old fogies," 



has dealt a telling blow to that cement. While I do not recant and 

 deny my just faith as to the efficacy of properly-prepared and pro- 

 perly-used white zinc, I submit that improperly-prepared white zinc, 

 in hasty, careless, or inexperienced hands, will prove treacherous, 

 and an exasperating failure. " Give us a good all-round cement," 

 says a Postal Club commentator. "Anything under the shining 

 sun," adds another. 



After an extended and critical experience, I can say that I think 

 that the cement prepared by Rev. J. D. King possesses all the desir- 



