6 STYLASTER1DAE 



which the stolons emerge. Examination of serial sections seems to suggest, that the endpderm in the 

 basal part itself is strongly vacuolated; but this may also be due to the imperfect state of preserva- 

 tion. The protoplasm is here strongly granulated and all indicates, that the albumen cells (cf. Schneider 

 1902 p. 579) form the principal mass of the endoderm in the basal part of the polyp, whilst the 



nutriment cells are in majority in the endoderm of the free wall of the 

 zooid. Apart from this localisation of the cell types the gasterozooid agrees 

 in the whole of its structure with the Hydroid polyp, as is clearly shown by 

 the figures (Text-fig. B, PI. Ill, figs. 28 and 29). Whilst the large cnidocysts 

 occur in fair numbers in the stolons, the small ones are concentrated in the 

 walls of the zooids. In the gasterozooids (PI. Ill, fig. 29) the cnidocysts are 

 Text-fig. B. The contracted accumulated densely in the ectoderm near to the month of the polyp and 

 gasterozooid of Pliobothrus entirely disappear further down on the polyp wall; in the dactylozooids they 



symmetricus. ec = ectoderm, 



en= endoderm, = mouth, are more uniformly distributed in the ectoderm in the whole length of the 

 th"d of th zooid) but become however less numerous near its basis. - To judge from 



= mouth of the gastero- Moseley's drawing (1881 PL VIII, fig. 2) the gasterozooid should have a wide, 



cruciform mouth in Pliobothrus symmetricus. The mouth of the polyp is 



closed in all the specimens examined from the "Ingolf" Expedition and is neither larger nor shaped 

 differently from that of the Hydroids generally. The cruciform appearance noted by Moseley is 

 clearly due to chance, for the protruding parts of the endoderm in the numerous sections examined 

 vary greatly in form, size and number. 



In their discussion of the family characters of the Stylasteridae Hickson and England state 

 (1905 p. 13): "The solid scalariform endoderm of the dactylozooids is another very distinctive feature 

 of the group". This does not hold good for Pliobothrus symmetricus; the dactylozooids have a distinct 

 lumen in their centre, as shown in transverse sections (PL IV, fig. 34). The authors cited maintain, 

 that "the scalariform tissue is clearly a much more differentiated tissue", -- naturally, under the tacit 

 assumption, that the dactylozooid is a reduced polyp. This would suggest, therefore, that Moseley's 

 view of Pliobothrus as a primitive genus of the Stylasteridae is correct. 



There is one condition, however, which seems to point in the opposite direction; this is the 

 male gonophores and their structure. Moseley indicated already, that their appearance differs from 

 that found elsewhere in the Stylasteridae. But his drawing (1881 PL VIII, fig. 3) is in so far misleading, 

 as it gives the impression, that the difference only consists in a denser accumulation of very small, 

 single gonophores. A series of sections through the male gonophores (PL IV, figs. 4042) shows ex- 

 tremely aberrant features. Each ampulla contains a single, fairly large, globular gonophore, which is 

 composed of a number of follicle-like portions (pseudofollicles); the reproductive cells are in extremely 

 different stages of development in the various pseudofollicles of the gonophore. The spadix as a rule 

 is slightly branched between the pseudofollicles and sometimes we find, that slender connecting bridges 

 lead from the stolons of the ampullar wall over to other parts of the gonophore wall than those where 

 its spadix connects with the stolons of the colony. - - Hickson (1891) has demonstrated the forma- 

 tion of a "seminal duct" in Stylasteridae where the male gonophores are of primitive structure. Such 

 a formation can certainly not be found in Pliobothrus symmetricus. The apex of the compound gono- 



