Mr. Rainey on the Stnicturc of the Cysticcrcus ccUulosse. 489 



shapes ; in others, these molecules are mixed with granules of 

 various sizes, which have every appearance of having been pro- 

 duced by the coalescence of the molecules ; and lastly, with these 

 molecules and granules, there are in other examples verj'^ distinct 

 globular cells, of a bright aspect, looking more like nuclei than 

 perfect cells ; these soon become flattened oval, and ultimately take 

 the elliptical form before described. All the time these changes are 

 taking place in the molecules and cells, the membrane has been in 

 progress of formation, so that when the molecules have disappeared, 

 and their place has become occupied by perfect cells, the end of the 

 animal is completed. The cilia are soon afterwards added. The 

 lateral growth of these animals takes place in the same manner: the 

 first indication is a separation of the cilia, which, it must be observed, 

 are larger at the sides of an entozoon than at the extreme ends ; 

 and then a thinning of the membrane supporting them ; and, lastly, 

 the formation of globular cells, as before noticed. After the animals 

 have become of a considerable size, and forced their way from the 

 interior of the primary fasciculi into the cellular spaces between ■ 

 the larger muscular fibres, they still continue to grow, especially 

 in breadth ; but they lose their cilia, and gradually acquire those 

 parts which have been described as belonging to the neck. The 

 first evidence of this addition is the appearance of inversion of the 

 middle part of the cyst, forming a small hollow, the sides of which 

 look as if thrown into folds containing granular matter, and the 

 bottom presents a circular space in which are granular jiarticles of 

 various forms and sizes, but those in the centre are darker than the 

 rest. It is from these particles that the suctorial disks, the hook- 

 lets, and the first of the laminated bodies are about to be formed, 

 but as yet none of these parts are recognizable. At a stage a little 

 more advanced, this apparent inversion of the cyst has increased, 

 the neck has become longer, and the appearance of disks, hook- 

 lets, and laminated bodies is sufficiently distinct to be perfectly 

 recognizable. The jirocess of development is particularly apparent in 

 the booklets, and perhaps there is no other instance of the growth of 

 an animal tissue which presents such facilities for the examination 

 of the manner in which it is effected. First, because the part of 

 the entozoon on which these organs are formed, is sufficiently trans- 

 parent to admit of examination by the highest magnifying powers 

 without any previous dissection. Secondly, because the material 

 of which they are composed is so characteristic, and so dissimilar 

 to the surrounding parts, that it can be detected in the minutest 

 possible quantities. And, thirdly, as only a few of these booklets 

 are in progress of development at one time, and as these are in all 

 stages of formation, every step in the progress of their growth can 

 be traced from the merest molecule to a perfect booklet. This is 

 important in reference to the general theory of development, as it 

 furnishes an example of the formation of a complete set of organs, 

 on a plan more simple, and at variance with the cell-theory of 

 Schwann and others. Before one of these booklets takes on a 

 rccognizat)lc form, it exists as a group of exceedingly refractive 



