THE SPOROZOA 313 



eider that the true systematic position of the forms is amongst the algae, 

 and their place amongst the Sporozoa is far from being assured. Within 

 the last decade, however, some other genera have been described which 

 are possibly related both to Amoebidium and to the true Sporozoa, and 

 the order may be retained provisionally for a collection of genera to which 

 it is difficult to assign a more definite position. The genera placed here 

 are best described separately. 



Genus 1. Amoebidium^ Cienkowsky, 1861. The forms composing this 

 genus differ in their habit of life from all typical Sporozoa and from any 

 species mentioned in the preceding pages, being ectoparasitic upon various 

 Crustacea or aquatic insect-larvae in freshwater. They were first discovered 

 by Lieberkuhn in 1856, who pointed out their affinities with "psoro- 

 sperms." Five years later they were the objects of detailed investigation 

 on the part of Cienkowsky, in whose opinion they were organisms of 

 vegetable nature. Other species were added to the genus by later 

 observers. 1 A. parasiticum, Cienk., the type-species (Fig. 125), occurs on 

 the branchial lamellae, antennae, carapace, etc., of Asellus aquaticus, 

 Gammarus pulex, and various freshwater Entomostraca, and upon 

 Phryganea and other aquatic insect-larvae, in the form of slender tubes 

 (Fig. 125, a-). At one extremity the organism is attached to the skin of 

 the host by a disc-like expansion, and immediately above this region the 

 body is slightly narrowed to form a short stalk, continued by the rest of 

 the tube, which is generally cylindrical and of even calibre, but may be 

 clubbed or exhibit other variations as regards external form. The wall 

 of the tube is a delicate membrane, which does not give the reactions 

 characteristic of cellulose. The contents of the tube consist of protoplasm, 

 containing fine granules, fatty spherules, and often vacuoles. The youngest 

 tubes contain a single nucleus, but in older individuals the nuclei multiply 

 as growth proceeds, and in full-grown tubes numerous nuclei are found 

 scattered at regular intervals along the whole length of the tube (Fig. 125, 

 a). The reproduction of Amoebidium is effected by two distinct methods, 

 which may, however, be combined in various ways. In the first place, 

 the contents of the multinucleate tube may be divided up by oblique 

 partitions passing between the nuclei, into as many uninucleate segments 

 or daughter -tubes as there were nuclei originally (Fig. 125, c). Each 

 daughter-tube (Fig. 125, &) may then grow into a multinucleate Amoebidium 

 again. In the second place, the whole contents of the multinucleate tubular 

 body, or of the uninucleate daughter - tubes either before or after they 

 have left the mother-tube, may become segmented along cleavage planes 

 running in various directions, into a number of uninucleate amoeboid 

 spores (Fig. 125, rf, e\ which soon begin to move about within the tube, 

 and finally escape from it at one point or another. The amoebulae or 

 "zoospores" (Fig. 125, f-h) thus liberated creep about for a time, but do 

 not appear to feed, and have no contractile vacuole. After a time, each 

 amoebula comes to rest, assuming first a spherical form, with one or two 

 large vacuoles internally, then it becomes oval and forms a cyst (Fig. 125, i-k). 

 In the warmer season of the year cysts are formed with a thin wall, within 



1 For references to the literature of the genus, see Biitschli [1], pp, 611-614, and 

 Labb6 [4], pp. 122, 123. 



