BROA D-LEA VED HORN WRA CK. 



235 



The wall of the zooecium is composed of a cuticle or ectocyst and an endo- 

 cyst. The former (e.) is chitinoid, and the chitin of the base of the two spines, of 

 the two ends with their angles, are strengthened by calcareous matter, and a cal- 

 careous plate also occupies the greater portion of each side. Each end is per- 

 forated in two places, each side in four places, by a set of pores. These pores are 

 grouped within circular areae with raised margins, and are known as ' rosette ' or 

 ' communication ' plates (r.}. The endocyst (/.) is thin and delicate. Over the 

 rosette plates it consists of columnar cells. Elsewhere it is membranous, containing 

 scattered nuclei surrounded by masses of protoplasm. Two cords of fusiform cells, 

 applied to the endocyst of the lower surface, connect the rosette plates at one end 

 with the corresponding plates at the other end. These cords anastomose inter se, 



C 



Fig. 10. A. Longitudinal section, magnified, of Membranipora (Flustra} membranacea, 

 after Nitsche. 



B. Avicularium (typical), after Hincks. 



C. Vibraculum of Scrupocellaria scruposa, after Hincks. 



and with the lateral rosette plates. Other cords, the funiculi laterales (/), com- 

 posed of superficial fusiform cells surrounding a granular axis, run from one to the 

 adjoining rosette plate, and are connected also to the funiculi of the stomach (_/".). 

 The fore-part of the body or tentacle-sheath 1 when retracted is contained 

 within the basal part. In Fig. 10, A. it is represented as fully expanded. Its 



1 The term 'polypide' is often used to denote 'the zooid, consisting of alimentary canal, 

 with tentacles, nervous ganglion, &c., which is developed within the zooecium ; ' and then ' zooecium ' 

 (=cell, auct ; cystid, Nitsche; Brutkapsel, Reichert) denotes 'the chamber in which the polypide 

 is lodged ' (Hincks). The term zooecium is used here and in the general account of Polyzoa to 

 denote the thickened part of the cuticle which persists after the death and decay of the rest of the 

 organism. It is simply a skeletal structure. The term polypide is discarded altogether. For the 

 view that a Polyzoon consists of two distinct animals, i.e. zooecium, and tentacle-sheath + digestive 

 tract, is now known to be erroneous, and the use of the word only tends to maintain the error. 



