338 The Parasites of the Cockroach. 



able examples of the power, inherent in animal life, of trans- 

 mutation of form under the influence of external circumstances 

 which zoological science reveals. Such varied phases of 

 existence as those to which the Tamiadee are subject go far to 

 support the view, independent of any general theory as to the 

 origin of species, that all animal parasites have been introduced 

 into the organisms which they inhabit at the first fortuitously, 

 and that, in the course of time, succeeding generations have 

 become more and more specialized and adapted for an entozoic 

 life. Many animals are inhabited by several forms of Entozoa at 

 the same time. Man himself is subject to the encroachments of 

 not less than thirty species ; and it is more than probable that 

 not a single individual exists among the higher forms of animal 

 life which is not inhabited by two or three parasitic species. 



The common cockroach [Blatta orientalis) is infested by 

 four Entozoa, which represent the four classes of animals whose 

 members are occasionally or always internally parasitic. These 

 four groups are the Monadina, the Gregarinida, the Infusoria, 

 and the Scolecida. If, when the hour is somewhat late, you 

 descend into the lower regions of your house, where the fire 

 still burning illuminates the kitchen with a sullen, dim 

 glow, you will find, as many know too well, a greater or less 

 number of these flat, ungainly-looking insects scuffling and 

 hastening over the floor ; some in dense groups devouring a 

 morsel of cheese or bread ; others hiding under the fender, or 

 basking in the liberty of the fire. Having secured a few in a 

 bottle, and brought them to the microscope, the search for En- 

 tozoa may be commenced by separating the abdomen length- 

 wise into two unequal portions, the insects being first deprived 

 of their consciousness by a few drops of chloroform. The whole 

 of the intestine with the gizzard will be exposed by the incision, 

 and portions of it may then be teazed out on a glass with a little 

 water and examined. 



Monadina. — Frequently the most numerous parasites in the 

 Blatta are the Bodos, which require a high magnifying power 

 to be observed. Their structure is very simple (PI. fig. 10), 

 being merely a cell containing a nucleated granule, and fur- 

 nished with a pair of minute, thread-like appendages, placed 

 opposite to one another, which are ever moving. Hundreds of 

 these little cells may sometimes be seen, waving their minute 

 cilia together. They bear a strong resemblance to the Sperma- 

 tozoa of higher animals, for which, indeed, they are sometimes 

 mistaken. The species found in the cockroach is the Bodo 

 Blattce, and is only the ,^tli of an mch in diameter. 



Oregarmida. — In teazing out the intestine of the insect, 

 little white translucent flakes may often be observed, which do 

 not measure more than ^tk of an inch in length. When 



