Porifera. C. Porifera calcaria. 



Homocoela , and strictly liomologoiis with the granulär ring round a prosopyle in 

 the Heterocoela«. — The second section are the Reticulata. The colony here forms 

 a more or less complex network of tubes; it is no longer possible to distinguish se- 

 parate individuals. Six types can be distinguished. — Type A. represented by 

 Lmcosolenia dubia n. The colony forms a loose network of tubes, without a com- 

 mon investing skin. — Type ß. Leucosolenia stipitata and imlcherrima. The 

 colony consists of a network of tubes which debouch in one or more main tubes. 

 The inside of the whole complex of tubes is lined by choanocytes. The peripheral 

 tubes are wide and the interspaces between them rather small. Hereby is formed 

 a kind of common outer wall (»pseudoderm«) with inhalant apertures (»pseudo- 

 porescc). Another remarkable modification is, that the strengthening spicules of 

 this »pseudoderm« are »of somewhat greater size« than those of the central parts 

 of the colony. — Type C. Leucosolenia cavatu n. Here we find a very striking 

 modification of the type B. The lowermost (older) portion of the colony consists 

 of a number of very simply branching and anastomosing tubes. The tubes are 

 narrow, the interspaces wide, so there is no »pseudoderm«. In the upper (younger) 

 portion of the colony, however, the peripheral tubes fuse together, and in this way 

 their outer walls form a »pseudoderm«, leaving between them small apertures, 

 »pseudopores«. At the same time, all the tubes increase in diameter and become 

 very irregulär, while the interspaces become constricted. The result is, that »the 

 tubes and the interspaces appear to have changed places entirely«. The author 

 calls this phenomenon »reversal of the canal System«. Thus the »pseudopores« 

 lead into more or less regulär tubulär canals , while the oscula communicate with 

 the irregulär wide Spaces , the iatter representing the widened original Ascon- 

 tubes, the inside of which is lined by choanocytes. On the other band are the 

 regulär tubulär canals lined on the out si de with choanocytes. Lendenfeld (^) 

 has apparently seen this, but not explained it. Dendy (^) found a communication 

 between the two Systems by means of small apertures, the original pores. — 

 Type D. Leucosolenia ventricosa (Crtr.). Here we find again a complex of Ascon- 

 tubes and a »pseudoderm«. But the inside of the main exhalant tube, terminating 

 in an osculum, is not lined by choanocytes. A great portion of this »pseudogaster« 

 is lined by pinacocytes. The author believes these cells to be ectodermal, and 

 considers the »pseudogaster« as lying »outside the colony and formed probably by 

 the upgrowth of the colony around it«. It is in this »pseudogaster« that the 

 Ascon-tubes open by the true oscula. — Type E. Leucosolenia proxima n. The 

 cloacal cavities of the Ascon-tubes are more or less subdivided into incomplete 

 Chambers by ingrowths of »mesoderm« which is not lined by choanocytes. Canal- 

 system resembles mostly type B., with exception of the ingrowths of parenchyme. 

 — Type F. Leucosolenia wilsoni n. shows a further development of type E. The 

 ingrowths are more strongly developed and lined by choanocytes. — Radiata. 

 The colony consists of a central tube from which smaller tubes are budded radi- 

 ally. Leucosolenia tripodifera (Crtr.) resembles a sack , the thick walls of which 

 are made up by a great number of radial tubes. At the top is a wide osculum, 

 and here there are no radial tubes, the wall being thin and perforated by pores. 

 » At a short distance below the osculum , however , small hoUow buds make their 

 appearance as outgrowths of the thin tube wall«. Lower down these »buds« are 

 larger and begin to ramify. They often touch and there is sometimes a communi- 

 cation between them. The whole central cavity with its diverticula is lined by 

 choanocytes. The outer surface of the sponge, i. e. the tops of the diverticula, is 

 protected by special spicules. Between the ends of the radial tubes there are 

 numerous (inhalant) apertures. 



