223 



Each lateral wall is divided into two planes, bent towards each other at an 

 angle (figs., 1 f, 1 g), and, excepting the one that separates the niother-zooecium 

 from the daughter-zocccinm in the bizooccial segment and which has in its proxi- 

 mal part more than 30 uniporous rosette-plates, each of these planes has to- 

 wards its centre a small group of 4 — 10 rosette-plates. Through the proximal of 

 these groups the zooecium directly communicates with the pedal chamber, and 

 through the distal one either with the scapular chamber only or with the infra- 

 scapular one as well, which is in many cases either not at all or only incom- 

 pletely separated from the former. The scapular chamber is generally developed 

 as an aviculaiium on both sides of the zoceciuni succeeding the mother-zoojcium 

 of the bizod'cial segment (fig. 1 a), and on the external side of the solitary zooe- 

 cium or zo(x;cia springing from the daughter-zooecium of the same .segment. If a 

 series of (up to 4) zoa^cia starts from the latter, one or several of them is often 

 provided with avicularia on either side; but only in very rare cases do we find 

 an avicularium on a bizooecial segment. The two avicularia occurring on the 

 same zoa'cium are generally of different size. This difference is however largest 

 in the zocrciimi springing from the mother-zod'cium of the bizoa'cial segment, 

 as the avicularium situated on the same side as the acute-angled corner of the 

 opening may be three times the length of the other. The avicularia, the ojier- 

 cular area of which has a strongly developed cryptocyst, have an angularly 

 rounded roof, rising outwards into a more or less steeply ascending, rounded and 

 pointed terminal part which in the large avicularium is very long and proxi- 

 mally to the distal point is furnished with a short hook. The roof of each avi- 

 cularian chamber is provided with 4 — 10 rosette-plates, which serve for commun- 

 ication between the avicularium and the supra-scapular chamber. The latter 

 has only meml)ranous outer walls, formed bj' two outwardly ascending mem- 

 branes, which meet at an acute angle and are separated from the avicularium 

 only by a low, arch-shaped calcareous ridge on each side. The large avicularium, 

 of the length of the zoa^ciuni, has its aperture turned obliiiuely towards the 

 frontal surface of the colony, while the aperture of the small avicularium is 

 turned in the opposite direction. While the large avicularium takes up the entire 

 distal plane the snuill one occupies only the distal half of the latter, but in such 

 a way thai all the rosette-plates are situated within its margin, whereas the 

 proximal wall of the avicularium forming the boundary towards the infra-scapular 

 chamber has 4 — (5 rosette-plates (fig. 1 d). Ajjart from the low, ridge-like calcareous 

 walls, which partly surround and i)artly separate them from each other, the 

 infra-scapular as well as the pedal chamber are only covered by a membrane. 

 But while the infra-scapular chamber corresponding to the small avicularium 



