Characteristics of Rhizopoda. clxv 



This membrane is not always demonstrable, and appears to be occa- 

 sionally wanting", as in Oxy trichina. The contractile vesicles may 

 be very numerous, as in Traclielius ovum, but ordinarily they are 

 not more than two in number. They are in some cases seen to give 

 off vessels into the body ; and they are said to communicate with 

 the exterior, and thus to become analogous to the water-vascular 

 rather than, as is often said, to the circulatory system of higher 

 animals. The so-called ' nucleus^ or ovary may vary in shape from 

 that of a spheroid to that of a horse-shoe. The ' nucleolus' or 

 testis is also very variable in shape, but is usually closely apposed 

 to or immersed in the substance of the ovary, which is much larger 

 in size. 



In sexual reproduction the ' nucleus' breaks up into a number of 

 ova, which it is probable are directly transformed into embryos. It 

 is often seen to be preceded by conjugation, in which the spermatic 

 elements of the two individuals have been supposed to be inter- 

 changed. 



Asexual reproduction takes place in the ways of gemmation, 

 when compound colonies may be formed, as in Episiylis and Car- 

 chesium; and of fission, which is ordinarily preceded by encystation. 



Class, Rhizopoda. 



Protozoa possessed of pseudopodia, by which, in the absence of 

 cilia, the functions of locomotion and of ingestion of aliment are 

 performed. Their bodies may consist of sarcode alone without any 

 morphological element except fine granules, and without any cell 

 wall ; and in these cases a calcareous shell may be secreted, as in 

 the majority of the Foraminifera, or a test of organic chitin-like 

 substance, as in Gromida ; or an external casing may be formed by 

 the agglutination of arenaceous particles, as in Lituolida; or the 

 sarcode may show considerable differences between its central and 

 peripheral layers, and may contain a nucleus and a contractile 

 vesicle, but be devoid of any externnl inorganic deposit of the 

 nature of a shell, as in Amoebina and Actinophryna ; or, finally, 

 the sarcode may be divided into two portions by a central capsule, 

 and be further supported by a siliceous skeleton, in which case 

 both the extra-capsular and the intra-capsular sarcode contains 

 many and various morphological elements, as in the multi-cellular 



