95 



The entoderm {eno.) constitutes the internal layer and faces the pericystic cavity {p.cav.) 

 ("Gastrovaskularraum" Chun). When describing more accurately the anatomy in the different 

 sections, we shall speak of it again. 



These three layers constitute together not only the outward wall of the pneumatophore 

 but also the body of all the appendages. Encircled in this e.xterior sac, is another one consistino- 

 of course of the same series of layers. As is universally admitted the pneumatosaccus constitutes 

 the invaginated proximal part of the pneumatocodon, its entoderm therefore is to be found 

 facing- the entoderm of the pneumatocodon or outer wall and the ectoderm is originally situated 

 on the opposite side lining the interior of the pneumatosaccus. On the opposite side of the 

 bunch of young appendages, this entoderm, fulcrum and ectoderm can be easily traced, the 

 pericystic cavity separating this pneumatosaccus from the pneumatocodon. On the side of the 

 young appendages we find that the narrowed proximal part or air-funnel sinks more or less 

 into the pericystic cavity and is dichotomously branched. Its supporting layer (fac.) corresponds 

 in some sections with the lulcrum of the pneumatocodon. Its ectoderm especially at the base 

 of these side-branches develops a great amount of secondary ectoderm, {sec. exy) which not 

 only appears in the air-funnel, but passing through the pneumatopyle (PI. XVII, fig. 124/. (?v 

 "Trichterpforte") spreads along the interior wall of the pneumatosaccus {exac) attaining its greatest 

 development near the pneumatopyle, gradually diminishing on both sides of the pneumatosac. 



In Cat. 22 it continues altogether and lines the whole interior wall of the pneumatocy.st. 

 This will be more fully described later on. 



In all three specimens the chitinous pneumatocyst constitutes the inner layer of the 

 pneumatosaccus (in Cat. 22 accompanied by secondary ectoderm) and often fits into folds of the 

 secondary ectoderm ; this is only the case in the secondary ectoderm in the pneumatosaccus 

 (PL XVII, figg. 126, 127, 128/./,!'). It ends on both sides of the secondary ectoderm in two 

 club-shaped enlargements (PI. XVII, fig. 124^./!'). 



As well as in the secondary ectoderm of other Physonecta (Athorybia, Physophora)^ so 

 well-described by Chun 97a, we found traces of the so-called giant-cells ("Riesenzellen") both on 

 the proximal and in the more distally situated secondary ectoderm (r.z.r.z.). Thev are marked 

 as small black granulations on PI. XVII, fig. 135 r.z. Together with these gigantic cells circular 

 cavities are found which are formed by the gas-secreting cells of the secondary ectoderm. Oi 

 these we shall also have occasion to speak later. 



The diagrammatic sketch gives one a general idea of the structure of the pneumatophore 

 of Archangelopsis typica, as we suppose it to be in the living state; it was made entirely from 

 the sections. We shall now describe a few of these in their successive stao-es 



Histologically, as we said above, very little has remained well-preserved. We will therefore 

 give again diagrammatic sketches. The first striking one is given on PI. XVII, fig. 125 I (gla.ss 

 10 III 8). We see to the left the bunch of appendages (<5. «.) most of them being cut in 

 longitudinal section. The ectoderm was almost entirely lost but has been added in the diaoram 

 for clearness' sake. That all these appendages {d.a.,6.a.) are not all cut longitudinally can 

 be seen by the two circular ones to the left, which in the next sections are found to join 

 the other appendages. It is also clear that the outer wall of the appendages passes apically 



