26 



OVUM. 



called by H. D. Goodsir ; and they have been cells, from which it is supposed other young 

 observed, in some instances, attached in pedi- animals or heads may be formed.* 

 culated vesicles, singly or in groups, to the inner 



Fig. 23. 

 Fig. 22. 



Echinococcus hominis. (From Wilson.') 



A and B, grouped and single Echinococci, at- 

 tached by peduncles to the inner membrane of the 

 cyst, c, a contracted, and D, an expanded Echino- 

 coccus; a, the peduncle. E, a more advanced 

 animal, shrivelled. 



surface of the cyst.* While enclosed in the 

 pediculated vesicles, the head of each echino- 

 coccus is retracted within the short vesicular 

 body in a manner which seems to be general 

 among the young of encysted Entozoa. They 

 are aftersvards set free, and in this state are 

 found floating as minute whitish particles in the 

 fluid of the cyst. They then present the appear- 

 ance of minute heads of Taeniae, with a short 

 body scarcely larger than the head ; the latter 

 part being furnished with a terminal double 

 circle of booklets, and four suckers.f 



The mode of gemmation may probably vary 

 in different circumstances, more particularly 

 in regard to the extent to which the progeny 

 of gemmation may or may not repeat the for- 

 mation of others of the same kind ; but every 

 thing that is known of the acephalocvstic 

 productions seems to point to the view that 

 they are all nearly allied, and that they are 

 abnormal or aberrant conditions of Taenia- 

 larvae, which, when they become encysted, are 

 incapable of development into the cestoid form 

 which belongs to those that have reached the 

 free intestinal habitation. 



The Casnurus, which has been met with 

 principally in the brain and some other parts 

 of the sheep and some other Ruminating ani- 

 mals, consists of a large cyst or vesicle with 

 a number of small heads projecting on its ex- 

 ternal surface: each head resembles closely 

 that of an echinococcus animalcule, presenting 

 the same circle of booklets and four suckers. 

 According to H. D. Goodsir, they are at- 

 tached to the middle membrane of the cyst, 

 from which they sprout at first, carrying the 

 outer one along with them : the neck contains 



* E. Wilson's paper in Med. Chir. Trans, xxviii. 

 1845 ; and H. D. Goodsir, Anat, and Path. Obs. 



f See Curling, in Med. Chir. Trans, vol. xxiii. ; 

 and Mttller, in Jahrsbericht of Archiv, 1836. p. 10G. 



Caenurus cerebralls, magnified. (After Bremser.} 

 , part of the general vesicle; b, an expanded 

 head ; c, a shorter head, showing the double circle 

 of booklets. 



The Cysticercus has been described in two 

 forms ; 1st, in its simply vesicular state, and 

 2nd, in its fasciolated condition, or in its 

 transition, as it may beheld, to the cestoid, or 

 tape form. The vesicular Cysticercus has 



Fig. 24. 



Cysticerci. 



A, Cysticercus longicollis (from Bremser), en- 

 larged. B, Cysticercus from the human eye (ex- 

 tracted by Dr. Mackenzie), magnified five dia- 

 meters. 



only one head ; but the structure of that part 

 is precisely the same as in the Caenurus 

 and Echinococcus, and, we may add, not 

 far different from that of the Taenia itself. 

 They are usually developed singly, that is 

 each vesicle with one head : but some ob- 

 servers f allege that they have seen internal 

 vesicles near the neck, which they look upon 

 as young, or as a progeny of gemmation in that 

 situation. 



The Cysticercus fasciolaris, as it has been 

 observed in the rat and mouse, presents the 

 remarkable fact of a Tsenia in various states of 

 development, from the vesicular condition of 



* H. D. Goodsir, loc. cit. 



f As Rose and II. D. Goodsir, loc. cit. 



