466 



Monday, \st April 1844. 

 Sir T. M. BRISBANE, President, Bart., in the Chair. 

 The following communications were read : — 



] . On the Development, Structure, and Economy of the Ace- 

 phalocysts of Authors ; with an Account of the Natural 

 Analogies of the Entozoa in general. By Harry D. S. 

 Goodsir, Conservator of the Museum of the Royal Coll. 

 Surg. Edin. Communicated by John Goodsir, Esq. 



The Acephalocyst or Hydatid is composed of a vesicle containing 

 fluid. It propagates by means of internal gemmules, which are de- 

 veloped between the layers of the membrane composing the vesicle, 

 and, after a certain time, are thrown off internally. 



The author, after pointing out these distinguishing characters of 

 the Hydatid, referred to the confusion which had arisen, from want 

 of proper observations on this point, and which, with other causes, 

 had been the reason why the animal nature of these creatures had 

 been denied by some writers of great authority. 



The author having procured a new form of Acephalocyst, was en- 

 abled, from his observations on its structure and economy, to deter- 

 mine several important points relative to the anatomy, physiology, 

 and natural history of the other species of the class. 



He characterised this new species of Acephalocyst as a compound 

 animal, inasmuch as one continuous membrane covered a complete 

 group or mass of the Hydatids. This membrane was described as 

 consisting almost entirely of tubuli, ramifying freely through it, and 

 a number of ovoid disks scattered at short intervals over its surface, 

 the edges of which were lined with minute open stomata, which 

 opened into the tubuli. The author looked upon these tubuli and 

 stomata as the organs of nutrition. 



Another membrane lay immediately beneath that already de- 

 scribed, and covered each Hydatid in particular. The body of the 

 Hydatid itself consisted entirely of a homogeneous mass of gelatine, 

 intersected by a number of very delicate septa. 



The author now described the mode of pi'opagation, which he 

 stated was analogous to that of the polyps, in so far, that, \st, there 

 was a number of ova thrown off for the extension of the parent 

 group ; and, 2c?, another generation for the extension of the species 

 generally. These ovules arose from the internal surface of the ex- 



