ECONOMY OF THE ACEPHALOCYSTS OF AUTHORS. 567 



We have thus in the Csenuri a much more complicated mode of development 

 than in the Acephalocysts. There must be, therefore, many forms of Cystic En- 

 tozoa which have hitherto escaped observation, for in nature all changes from one 

 form to another are gradual. 



In the course of my observations on the structure and economy of the spe- 

 cies in the order of Cystic Entozoa, I was much struck with the analogies which 

 existed between the various forms of the class, and those of other classes of the 

 animal kingdom ; and as I look upon these to be particularly important in estab- 

 lishing my views relative to the animal nature of the simple Hydatid, as well as 

 in determining the limits of the class, I shall now submit them to the considera- 

 tion of the Society. 



Beginning with what I conceive to be the lowest form of Entozoon at present 

 known, the simple Hydatid, I find in it the analogue, in its own class, of the typi- 

 cal forms of the Infusoria as the Volvocinse. 



Proceeding to the new form of Hydatid, which has been described in the 

 preceding part of this paper, I consider it as the analogue of the Polypifera, and 

 of such forms as have Alcyonidium for their type. In both we find the same 

 general basal mass, and the same mode of nutrition, in the Hydatid, by means of 

 disk-bearing stomata each disk analogous to a polype and in the Alcyonidium 

 by tentaculated heads with stomach cavities. Both forms also are compound, the 

 general group deriving nourishment from the individuals, and the individuals 

 deriving support from the group ; so that, in both cases, the general mass and indi- 

 vidual stomata or polyps mutually tend to support one another. Both have two 

 modes of propagation one for the extension of the original group, the other for 

 the establishment of other groups. 



The Echinodermata are represented among the Entozoa in a curious and in- 

 teresting manner, by the suctorial forms of that class ; that is, by those forms of 

 Entozoa which are endowed with these organs as a means of adhesion or progres- 

 sion, such as Distoma, Tristoma, &c. The lowest form in this suctorial tribe is 

 the Diplozoon Paradoxum of Nordman. I am inclined to consider Diplozoon as 

 inferior to Distoma and other suctorial forms, not from its analogies, but from 

 this circumstance, among others, that its whole organization is double, and con- 

 sequently less centralized. The Asteriadse, among the Echinodermata, are repre- 

 sented in the Entozoa by Diplozoon and other similar forms, which undoubtedly 

 exist. The Tristomse (PL XV., fig. 9) are represented by the flat Echinidse, as the 

 Scutellse. (PI. XV., fig. 8.) In both the Tristoma and its Echinodermatous ana- 

 logue, the Scutella, we find the disk imperfect in certain parts of its edge, indi- 

 cating the remains of a more divided or asteroid condition of the body. The 

 Distomse are the analogues of the true Echinidse. A starfish folded up upon 

 itself, so that the tip of its rays meet at one central point, constitutes that form 

 of the Echinodermata known as the Echinus. In like manner, among the En- 



