561 ) 



XXXVII. On the Development, Structure, and Economy of the Acephalocysts of 

 Authors ; with an Account of the Natural Analogies of the Entozoa in General. 

 By HAKRY D. S. GOODSIR, Conservator of the Museum of the Royal College 

 of Surgeons in Edinburgh. 



(R*ad 1st April 1844.) 



THE Acephalocyst, or simple Hydatid, is composed of a vesicle, containing a 

 watery fluid, which, in the normal state of the creature, is quite transparent 

 and colourless (PI. XIV., fig. 1.) The internal surface of the vesicle is generally 

 studded with numerous cells of various sizes, many of which are found de- 

 tached and floating loose in the fluid contained in the vesicle. These are the 

 young Hydatids.* Their development will be described when we come to that 

 portion of the present paper, which has been set apart for that purpose. 



Hydatids, like the other entozoa, are incapable of sustaining an independent 

 existence, although, as independent creatures, they are similar to the other species 

 of entozoa. They infest all parts of the body, and are commonly lodged in cavities 

 containing fluid in Avhich the hydatids float. 



From two circumstances, the true nature of hydatids has been very much 

 misunderstood. The first, depending on imperfect observation, has arisen from 

 specific characters being unattended to, and consequently, from external resem- 

 blance alone, these animals have been erroneously classed with other and very- 

 different pathological appearances, such as serous cysts.f The second cause of 

 misunderstanding has arisen from the limited number of known species prevent- 

 ing naturalists from arriving at any general views with regard to their proper 

 relations. Both of these circumstances have doubtless retarded our progress 

 towards proper conclusions relative to their true nature, and, at the same time, 

 afforded reasons in support of the views advocated by those who denied the ani- 

 mality of the Acephalocyst. 



I am indebted to the kind attention of Dr GAIRDNER, for an opportunity of 

 examining a species of hydatid, which appears to have been hitherto undescribed, 

 the study of which has enabled me to detect several important circumstances re- 

 lative to the economy of the Acephalocysts, and also to trace out generally the 



* Vide MONRO'S Morbid Anatomy of the Gullet, Stomach, and Intestines, p. 198 ; also Dr JOHN 

 HUNTER'S paper, in the 1st vol. of the Transactions of a Society in London for the Advancement of Medical 

 and Chirurgical Knowledge. 



f HODGKIN. Transactions Medico-Chirurgical Soc. London, vol. xv. p. 266. HODGKIN. Lectures 

 on Morbid Anatomy, vol. i. p. 180, Lecture VII. 



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