MICROSCOPIC FORMS OF ANIMAL LIFE. 



35 



network of extreme tenuity (Fig. 298). Besides these branching prolon- 

 gations there is sent off from the central protoplasmic mass a broad, 

 thin, irregularly quadrangular extension (Fig. 297 B,-/), which extends 

 to the superficial rod-like ridge, and seems to coalesce with it; its lower 

 free edge has a thickened border; whilst its upper edge becomes continu- 

 ous with a plate-like striated structure, g, which seems to be formed by a 

 peculiar duplicature of the body-wall. At one side of the protoplasmic 

 mass is seen a spherical vesicle, h, of about 3-2000ths of an inch in diam- 

 eter, having clear colorless contents, among which transparent oval 

 corpuscles may usually be detected. This, from the changes it undergoes 

 in connection with the reproductive process, must be regarded as a 

 nucleus. 



428. The particles of food drawn into the mouth (probably by the vi- 



Fig. 298. 



Portion of superficial protoplasmic reticulation, formed by ramification of an extension a, of 

 central mass. Magnified 1000 diameters. 



brations of the flagellum) seem to be received into the protoplasmic mass 

 at the bottom of the oesophagus by the extensions of its substance, which 

 envelop them in filmy envelopes that maintain themselves as distinct from 

 the surrounding protoplasm, and thus constitute extemporized digestive 

 vesicles. These vesicles soon find their way into the radiating extensions 

 of the central mass (as shown in Fig. 297, A, B), and are ensheathed by 

 the protoplasmic substance which goes-on to form the peripheral network 

 (Fig. 299). Their number and position are alike variable; sometimes 

 only one or two are to be distinguished; more commonly from four to 

 eight can be seen; and even twelve or more are occasionally discernible. 

 The place of each in the body is constantly being changed by the contrac- 

 tions of the protoplasmic substance; these in the first place carrying it 

 from the centre towards the periphery of the body, and then carrying it 

 back to the central mass, into whose substance it seems to be fused as 

 soon as it has discharged any indigestible material it may have contained, 

 which is got rid of through the mouth. Every part of the protoplasmic 

 reticulation is in a state of incessant change, which serves to distribute 

 the nutrient material that finds its way into it through the walls of the 

 digestive vesicles; but no regular cyclosis (like that of plants) can be oh- 



