88 THE ANATOMY OF INVERTEBRATED ANIMALS. 



sporangium of Mucor divides into spores) into small bodies, 

 each of which acquires a spindle-shaped case, and is known 

 as a pseudo-navicella. On the bursting of the cyst these 

 bodies are set free, and, when placed in favorable circum- 

 stances, the contained protoplasm escapes as a small active 

 body like a Protamoeba. M. E. van Beneden has recently dis- 

 covered a very large Gregarina ( G. gigantea\ which inhab- 

 its the intestine of the lobster, and his careful investigation 

 of its structure and development has yielded very interesting 

 results. 



Gregarina gigantea attains a length of two-thirds of an 

 inch. It is long and slender, and tapers at one extremitv, 

 while the other is obtuse, rounded, and separated by a slight 

 constriction from the rest of the body, which is cylindroidal. 

 The outer investment of the body is a thin structureless cu- 

 ticle ; beneath this lies a thick cortical layer (ectosarc), dis- 

 tinguished by its clearness and firmness from the semifluid 

 central substance (endosarc), which contains many strongly- 

 refracting granules. In the centre of the body, the ellipsoid 

 " nucleus," with its " nucleolus," fills up the whole cavity of 

 the cortical layer, and thus divides the medullary substance 

 into two portions. The body of this Gregarina may present 

 longitudinal striations, arising from elevations of the inner 

 surface of the cortical layer, which fit into depressions of the 

 medullarv substance : but these are inconstant. On the other 

 hand, there are transverse striations which are constant, and 

 which arise from a layer of what are apparently muscular 

 fibrillse, developed in a peripheral part of the cortical layer, 

 immediately below the cuticle. The fibrillae themselves are 

 formed of elongated corpuscles joined end to end. A trans- 

 verse partition separates the cephalic enlargement from the 

 body, and the layer of muscular fibres only extends into the 

 posterior part of the enlargement. 



The embryos of Gregarina gigantea, when they leave 

 their pseudo-navicella?, are minute masses of protoplasm simi- 

 lar to Protamoebm, and like them devoid of nucleus and con- 

 tractile vacuole. They soon cease to show any change of 

 form, and acquire a globular shape, the peripheral region of 

 the body at the same time becoming clear. Next, two long 

 processes bud out from this body ; one is actively mobile, the 

 other still. The former, detaching itself, assumes the appear- 

 ance and exhibits the motions of a minute thread-worm, 

 whence M. van Beneden terms it a pseudo-filaru t. The en- 

 largement at one end becomes apparent, the pseudo-fiiaria 



