134 



THE RISE OF ANIMAL LIFE 



Fig. 7-28. A stalked-ciliate, Vort'icella, in various stages 

 of its life history. The two animals to the left are 

 undergoing division while on the extreme right is 

 the free-swimming stage which enables the species 

 to spread to new environments. The fine contractile 

 thread which can be seen in the stalk makes it pos- 

 sible for them to suddenly become coiled as some 

 of the organisms here. This is a plastic model. 



ered by man, the recent antibiotics and sul- 

 fas included. During the past war our sup- 

 plies of quinine were cut off, so we had to 

 rely on substitutes such as atabrine and 

 plasmochin. The problem of synthesizing 

 quinine went ahead during the war years 

 with unrelenting vigor until finally it was 

 successfully accomplished by the war's end. 

 At present, however, natural sources are 

 used since they are cheaper than the synthe- 

 tic product. A constant search is made for a 

 new specific for malaria and some success is 

 reported from time to time. Perhaps the 

 ideal one will be found in the future. 



Class Ciliophora 



The members of this class are distin- 

 guished by the possession of cilia and two 

 or more nuclei. These characteristics were 

 observed in paramecium, which is a repre- 

 sentative of this group. The class has been 

 subdivided according to the arrangement 



of the cilia into four orders, the more in- 

 terestino; members of three of these will be 

 described briefly. 



Those belonging to the order Holotricha 

 possess evenly distributed cilia over most of 

 their body. Paramecium is typical. 



Didinitim is an interesting member of 

 this group because of its carnivorous habits. 

 It is oval-shaped, with two bands of cilia 

 encircling the anterior and posterior regions 

 (Fig. 7-26). Protruding from the ante- 

 rior end is a formidable-looking proboscis 

 which is an effective organelle for impaling 

 paramecia prior to engulfing them. The 

 magnitude of this feat can be realized by 

 imagining a man eating a full-grown horse 

 at one sitting. This is only one illustration 

 of the voraciousness of these carnivorous 

 ciliates which abound in almost any stag- 

 nant water. 



The order Spirotricha includes a large 

 variety of diverse ciliates, one of which, 

 Spirostomiim, is a veritable giant among 

 the Protozoa. This cell reaches a length of 

 3 millimeters and can easily be seen with 



Fig. 7-29. Anton leeuwenhoek (1632-1723) was the first 

 man to see and describe many Protozoa as well as 

 other microorganisms. He was not trained in science, 

 but his devotion to the disciplines of the field places 

 him among the foremost scientists of his day. 



