EEPRODUCTTON OF GREGARINA. — THALASSICOLLIDA. 449 



acetic acid. Cilia have been detected both upon the outer and 

 the inner surface ; but these would seem destined, not so much to 

 give motion to the body, as to renew the stratum of fluid in contact 

 with it ; for such change of place as the animal does exhibit is 

 effected by the contractions and extensions of the body generally, 

 as in the Amceba (§ 332). An 'encysting process,' very much 

 resembling that of the lower Protophytes (§§ 188, 189), is occa- 

 sionally observed to take place in Gregarince, and seems to be pre- 

 paratory to their multiplication. Whatever the original form of 

 the body may be, it becomes globular, ceases to move, and becomes 

 invested by a structureless 'cyst,' within which the substance of 

 the body undergoes a singular change. The Nucleus disappears ; 

 and the sarcodic mass breaks up into a series of globular particles, 

 which gradually resolve themselves (as shown at b, c, Fig. 236) 

 into forms so like those of Naviculce (§ 233) as to have been mis- 

 taken for them ; though their walls are destitute of silex, and 

 there is no further resemblance between the two kinds of bodies 

 than that of figure. These ' pseudo-navicelhe ' are set-free, in 

 time, by the bursting of the capsule that encloses them ; and they 

 develope themselves into a new generation of Gregarinae, first 

 passing through an Amoeba-like form. A sort of 'conjugation' 

 has been seen to take place between two individuals, whose bodies, 

 coming into contact with each other by corresponding points, first 

 become more globular in shape, and are then encysted by the for- 

 mation of a capsule around them both ; the partition-walls between 

 their cavities disappear ; and the substance of the two bodies be- 

 comes completely fused together. As the product of this ' zygosis ' is 

 the same as that of the ordinary encysting process, there seems 

 no reason for regarding it, like the ' conjugation ' of Protophytes, 

 as a true Generative act ; and the resolution of the sarcodic body 

 into ' pseudo-navicellae ' must thus be regarded as analogous to the 

 resolution of the endochrome-mass of an Achlya or Ulva into 

 Zoospores (§§ 241, 247).* 



336. Thalassicollida. — A very curious type of Composite 

 Khizopods has been discovered by Prof. Huxley, which seems to 

 connect the preceding forms with Sponges and Polycystina. The 

 Thalassicollce , or Sea-jellies, are gelatinous rounded bodies, of 

 very variable size and shape, but usually either globular or dis- 

 coidal. Externally they are invested by a layer of condensed 

 sarcode, which sends forth pseudopodial extensions that commonly 

 stand out like rays, but sometimes inosculate with each other so as 

 to form networks. Towards the inner surface of this coat are 

 scattered a great number of oval bodies resembling cells, having 

 a tolerably distinct membraniform wall and a conspicuous round 

 central nucleus, thus corresponding closely with the Gregarina 



* For the most recent information on this point, see a Memoir by 

 M. Nat. Lieberkuhn in Mem. de 1'Acad. Roy. de Belgique, torn. xvi. 



G Q 



