80 SYM OPTIC COLLECTION. 



Cliona. This marble lay in water seven years, during 

 which time the borings from one and a half to two inches 

 in depth were made. 



Dr. Leidy 1 states that the large and numerous shells of 

 the dead oysters in an extensive bed planted by Beasley 

 at Great Egg Harbor, were so completely riddled in two 

 years by the Cliona that they were crushed with ease. 



The process of boring is both mechanical and chemi- 

 cal, and the habit seems to be an acquired one which has 

 been transmitted, Nassonow 2 stating that the young begin 

 to bore before the formation of the spicular skeleton. 

 The body puts forth fleshy outrunners and it is largely 

 these that do the work. . It is also probable that an acid 

 is secreted which aids in the work. Unlike most sponges 

 the Cliona discharges its eggs into the water before the 

 formation of the embryo has begun, so that the whole 

 development goes on outside the parent. 



The skeleton is made up of one rayed spicules, many 

 of which are pin-shaped. Ryder^ has shown that the 

 protoplasm in sponges executes delicate fluctuating move- 

 ments, so that in Cliona as in Stylocordyla and many 

 other genera, the needles are drawn into bundles or rows 

 extending in particular directions. 



In the fresh-water sponges (Spongilla, No. 83) the 

 silicious spicules are numerous, while a small quantity of 

 spongin is developed. These sponges, although probably 

 derived from some marine form, yet develop a structure 

 which is never found in the latter ; namely, the statoblasts 

 or winter buds. These are internal buds which are 

 enclosed in horny cases with peculiar spicules. When 

 the sponge dies the winter buds survive ; these are so 

 slightly affected by heat or cold that by them the perpet- 

 uation of the species is rendered more sure. In addition 



iProc. Acad. Nat. Sci. Phila., VIII, 1857, p. 162. 

 2 Zeitschr. f. wiss. Zool., XXXIX, 1883, p. 300. 

 3 Amer. Nat., XIII, May, 1879. 



