Neiv Species of Coenopsarnmia from Lifu. 73 



appearance and mode of development of the thread are strikingly 

 similar to those of elastic fibres in the higher Vertebrates. 



The mesenterial nematocysts are rather larger than the ten- 

 tacular and have a very thick thread, spirally coiled with about 

 8 turns. The thread ends freely in an invaginated portion at the 

 end of the nematocyst, which forms the base of the everted thread. 

 This basal portion, when everted, is seen to be covered with a 

 spiral row of hairs, and appears to be carried out by the basal 

 end of the thread on eversion. The whole nematocyst is not 

 extruded. The thread is broken off at a short distance from the 

 base, which is then retracted, a fresh thread being formed in the 

 nematocyst. Some of the nematocysts have well-formed nuclei. 

 The mesenterial nematocyst, indeed, is comparable to the cnido- 

 blast of Hydra together with its included nematocyst, while the 

 tentacular nematocyst is only comparable to the nematocyst of 

 Hydra. 



The ectoderm of the stomodoeum is very thick and has over 

 the attachments of the mesenteries rows of goblet-like secretory 

 vacuoles. These are directly continuous into the middle parts of 

 the mesenterial filaments, the lateral parts of which are sharply 

 marked off from the endoderm of the mesenteries. The whole 

 filaments from the anatomy appear to be ectodermic in origin 

 and formed by down-growths from the stomodoeum. 



The stomodoeum together with the mesenterial filaments 

 performs the main digestive functions and is hence the homologue 

 of the whole gut of the Triploblastica. The so-called endoderm, 

 giving rise to the muscular bands and generative organs, and per- 

 forming also the excretory functions, is homologous with the 

 mesoderm. 



In the terms of the larger theory the Actinozoon polyp must 

 then be regarded as also a Triploblastic form with definite ecto- 

 derm, endoderm and mesoderm. 



The full paper on this subject, with illustrations, will appear in 

 Part IV. of Dr Willey's Zoological Results. 



