GREGARINA, 97 



condensation of reproductive possibilities, may produce ova which 

 develop parthenogenetically. 



Here, then, we have an organism, on the border line between plant 

 and animal life, just across the line which separates the unicellular from 

 the multicellular, illustrating the beginning of that important distinc- 

 tion between somatic or body cells and reproductive cells, and occurring 

 in asexual, hermaphrodite, and unisexual phases. Klein records no less 

 than twenty-four different forms of V. anrciis from the purely vegetative 

 and asexual to the parthenogenetic, for there may be almost entirely male 

 colonies, almost entirely female colonies, and other interesting transi- 

 tional stages. Klein has also succeeded to some extent in showing 

 that the occurrence of the various reproductive types depends on outside 

 influences. 



Fifth Type of Protozoa GREGARINA. 



Gregari?ia, a type of those Sporozoa in which the cell is 

 divided into two regions by a partition. 



Description. --Various species occur in the intestine of 

 the lobster, cockroach, and other Arthropods. When young 

 they are intracellular parasites, but later they become free in 

 the gut. They feed by absorbing diffusible foodstuffs, such 

 as peptones and carbohydrates, from their hosts, and store 

 up glycogen within themselves. In many the size is 

 about one-tenth of an inch. There is a firm cuticle of 

 " protoelastin," which grows inwards so as to divide the 

 cell into a larger nucleated posterior region and a smaller 

 anterior region, and also, in the young stage, forms a small 

 anterior cap. The cell substance is divided into a firmer 

 cortical layer and a more fluid central substance. The 

 protoplasm often presents a delicate fibrillar appearance, 

 suggesting that of striated muscle. The nucleus is very 

 distinct, but there are no vacuoles. We may associate the 

 absence of locomotor processes, " mouth," and contractile 

 vacuoles, as well as the thickness of the cuticle and the 

 general passivity, with the parasitic habit of the Gregarines. 

 It is not clearly understood how these and other intestinal 

 parasites have become habituated to resist the action of 

 digestive juices. 



Life history.- -The young Gregarine is parasitic in one 

 of the lining cells of the gut ; it grows, and, leaving the 

 cell, remains for a time still attached to it by the cap 

 (Fig. 43, a.yg.} ; later this is cast off, and the individual 

 becomes free in the gut, while still increasing in size. Two 



