47 



eggs, this function in otiier forms is in charge of special individuals, which may 

 often differ greatly from the ordinary zooecia (Adeonidae, Catenariidae, certain 

 Hippothoa species), and which occasionally have no polypide (Hippothoa /iy«/i/ia). 

 They are in most cases furnished with separate marsupial clianihers, the so- 

 called oci'cia. 



I may now make some mainly comparative observations on the structure of 

 the Heterozocrcia. It we look at the frontal surface of an avicuiarium, the oper- 

 culum (or mandible) of which has been removed, we find that a greater or lesser 

 part of this surface is occupied by an aperture covered by a membrane, within 

 which there is often found a more or less developed cryptocyst. This part corre- 

 sponds with the membranous area in the zooecia of a Meinhninipora, but while 

 such an area in the zocrcia is only found in the division Mulacostega, it is found 

 in the avicularian chamjjer in all Cbeilostoniatous Bnjozoa. We may further 

 discern between two different parts of this area, a distal, the opercular area, 

 which is covered by the operculum and a proximal, the subopercular area, and 

 the border between the two areas is formed by the hinge-line, which coincides 

 with the proximal edge of the operculum. This border is in all Ascopbora with 

 the exception of the Adeonidae and of Leicschava criistacen also indicated by a 

 calcareous cross-bar, arising from the prolongation and amalgamation of the two 

 hinge-teeth, and besides in the genera Nellia, Finiilina, Arachnopnsia, Miciopura, 

 Microporina and a few Meinbraniporina (e. g. in M. crassiinaryinfdd) species, in 

 which such a cross-bar is also present, the two hinge-teeth are separated in 

 all other Anaska. Waters has already called attention to this difference. 



The cryptocyst, which can be present both in the opercular and the sub- 

 opercular area reaches its highest development in the heterozoa>cia of the genera 

 Onychocelld ' and RluKjasostomii, the former of which is mainly and the latter 

 exclusively represented by extinct species. The cryptocyst is here, as in certain 

 fossil species, which for the present I refer to the genus Aspidostoma (PI. VI c, 

 figs. 3 a, 4 a), extended over tbe greater part of the frontal wall of the chamber 

 and is only provided with a small opening of varying shape, which is intersected 

 by the hinge-line of the operculum and through which the muscles make their 

 way out to the operculum or mandible. In the avicularia of Fliistra foliacea the 

 cryptocyst extends over most of the subopercular area and something similar takes 

 place in the avicularia in several Thalamoporella species (Fl. VI a). A well- 

 developed cryptocyst is also found in the opercular area of the large avicularia 

 in Flustnt (dujssicola as well as in that of the large lyriform or spoon-shaped 



.S(), PI. 07.'), ligs. 2, 15. 



