141 



V. — StatoUasts of Fresh-water Poly:.oa. 



By C. F. EOUSSELET. 



{Exhibit and Demonstration, January 19, 191G.) 



Statoblasts are the most characteristic structures in the repro- 

 duction of fresh- water Polyzoa. Their form is very stable (except 

 in closely allied species), and each group has characters of its 

 own by means of which it can readily be recognized, even when 

 no trace of the adult polyp or the zooecium has been preserved. 

 Statoblasts are confined to tlie phylactolffimatous Polyzoa ; the 

 other fresh-water species, such as Victorella, Pedudicclla, Pottsiella, 

 Urnatella and Hislopia do not produce them, nor do they occur 

 in any of the marine species. 



The statoblasts are essentially non-sexual resting buds formed 

 in a structure called the " funiciilus " to tide over the risiiour of the 

 winter. In most cases they consist of a central capsule sur- 

 rounded by air-cells or swimming-ring, which renders the structure 

 buoyant, and enables the statoblast to float on the surface of the 

 water when liberated by the decay of the zooecium. In this way 

 a wide distribution and preservation of the species is secured at 

 the same time. 



On the appearance of warmer weather the young polyp, in an 

 advanced stage of development, splits open the cellular envelope 

 at the edges. This is effected in different ways in different species. 



Cridafella has a circular statoblast with numerous hooked 

 spines attached to both the surfaces. In emerging the embryo 

 lifts the lid, like a pill-ljox with a flange attached, and the hooks 

 are then seen to be attached, some to the lid and some to the base 

 of the box. 



In Pectinatella, which has fewer but larger hooked spines, the 

 opening takes place along the margin of the statoblast, and even 

 the spines are divided and split horizontally. 



Lophopus crystalliniis has a statoblast pointed at botli ends, 

 whilst in Lophopus capensis the ends are prolonged into elongated 

 hooked structures ; in opening the splitting takes place through 

 the length of these structures, leaving the hooks partly adherent to 

 the upper and partly to the lower half 



In Lop>ho2wdella, also, the splitting takes place through the 

 length of the finger-like processes, with the hooks attached to each 

 half of the processes. 



Fredericella differs frOni the other forms in tliat its statoblasts 



