ENTOPROCTA. 95 



the formation of this organ, assumecl it to be the first bud that attains develop- 

 ment in the larva. According to the more recent researches of Hakmer (No. 5) 

 and Seeliger (No. 12), however, it can no longer be doubted that the rudiments 

 of the buds only appear later, after attachment has taken place, and in another 

 way, and that therefore Hatschek's view was erroneous. Harmer, who traced 

 the origin of the similarly formed, bilobate, dorsal organ of Loxosoma, which is 

 jirovided Avith two pigmented eye-spots, explains it as a brain (supra-oesophageal 

 ganglion) arising through an ectodermal invagination and connected with a 

 sensory apparatus, and, further, united by fibrous commissures with the ganglion 

 that develops between the mouth and the anus. The latter is assumed by 

 Harmer to be the sub-oeso2)hageal ganglion (comparable to the pedal ganglion 

 of the Mollusca). 



Ill the later stages, the cup-like cavity known as the atrium t>r 

 vestibule (Fig. 45 A, v) forms in the Pedicellina larva, the oral 

 ciliated surface becoming more and more depressed. The floor of 

 the cavity thus formed soon shows a deep depression extending 

 between tlie mouth and the amis (Fig. 45 A), from the wall of 

 which the sub-oesophageal ganglion is said to originate as a simple 

 thickening of the ectoderm (Harmer) The lateral walls of this 

 depression separate it from an outer groove in the floor of the 

 vestibule; this latter groove runs round the anal cone and passes 

 over anteriorly into the funnel-shaped oral aperture. This groove 

 corresponds to the tentacle-groove of the adult. The outer thickened 

 edge of the cup that has thus arisen now becomes separated by a 

 furrow from the rest of the body-surface, and develops a massive 

 ciliated ring (Fig. 45 B), Avhicli functions as the locomotory organ 

 of the larva. 



As the muscle -fibres develop, the diff"erent parts of the body 

 become markedly retractile. The floor of the vestibule, especially, 

 can be protruded far beyond its aperture and again withdrawn. 

 When the larva is in the condition of greatest expansion, two 

 conical processes can be seen projecting from the aperture of the 

 vestibule (Fig. 45 B). The posterior cone carries at its apex 

 the anal aperture (a, anal cone), while the anterior process is distin- 

 guished by a tuft of long flagella ; this latter process has the same 

 position as the epistome, as it lies behind the oral aperture at the 

 anterior edge of the deep depression mentioned above. 



A feature of morphological importance is the presence of an 

 excretory apparatus {7iph) consisting of two small ciliated canals 

 which, in position and structure, agrees with that of the adult 

 (F'ig. 48, ex). We may compare this with the head-kidney of the 

 Trochophore larva of the Annelida. It opens externally aita,^i:^ppx\ 

 between the epistome and the ganglion. /C'^ '"^ '^ /\ 



[ujI LIBR AR Yj3o 



