DEVELOPMENT OF EMBRYO. 73 



exactly the same structures (cestoid heads = scolices). The latter 

 I have divided, in opposition to the Cysticerci, into platycercal 

 and acercal forms. Without flattering myself that I can conclu- 

 sively settle the question, " whether we have any external means 

 of predicating what Taenia must and will pass through a true 

 cysticercal } or a more or less cystercoidal state" I may be allowed, 

 nevertheless, to call attention to the following points, and, at the 

 same time, I take little notice of the fact that true Cysticerci 

 only occur in warm-blooded animals, especially mammalia, and 

 cysticercoid structures principally in cold-blooded animals. 



1. The eggs of all Taeniae which pass a true cysticercal stage 

 in the bodies of mammalia, are distinguished, not only by their 

 small size and the small size of the embryo and its six hooks, but 

 also by their brown, hard shell, beset with asperities externally, 

 which, in a certain position of the microscope, give the egg-shell 

 the appearance of a kind of concentric stratification, which, how- 

 ever, is only an optical appearance. The eggs of the Taeniae, with 

 only a cysticercoid phase of development, have softer, colourless, 

 transparent shells, are much larger, and contain a much larger 

 embryo, furnished with larger hooks. 



2. The Tarda with a cysticercal phase of development are 

 inferior to the platycercal and acercal forms in regard to the 

 length and cylindrical form of the rostellum. 



3. The Taenia with a cysticercal stage all possess during this 

 a highly-developed receptaculum capitis, which forms a part of the 

 future neck, in which, as long as this stage lasts, the head is 

 introverted, and which must not be confounded with Von Siebold's 

 receptaculum scolicis, the true caudal vesicle. The allied platy- 

 cercal and acercal forms are destitute of the accumulation of 

 water, and of the receptacidum. 



If, now, a cestoid vesicle which has immigrated into a suitable 

 host, and which originates from a Taenia which passes through a 

 vesicular state, being disturbed or entirely stopped in its pro- 

 liferation by any cause, remains sterile, it becomes converted 

 into an Acephalocyst. Such as were destined to become true Cys- 

 ticerci then possess in their walls the structure of the cysticercal 

 caudal vesicle ; and those which should have become Echinococci 

 exhibit in their walls the concentric structure of the Echinococcus- 



und Blasen-wurmer,' Leipzig, 1854, "that he has obtained T. serratahythe administra- 

 tion of Coenurus cerebralis to dogs. But these three species also differ in respect of the 

 results of administration." 



