larvae are ready to emerge. The capsule is oval, elongate, or some- 

 what bean shaped, and one of its edges is usually serrate. The young 

 are in some instances assisted to escape by the parent, who with her 

 feet aids in splitting the capsule on the serrate edge to facilitate their 

 exit. On hatching, it is said the young are often kept together by the 

 parent and brooded over and cared for, and at least a colony of young 

 will usually be found associated with one or two older individuals. 

 These insects are more or less gregarious, notably so in the case of the 

 black beetle of Europe and to a less extent with the German and 

 American roaches. 



They pass tlirough a variable number of molts, sometimes as many 

 as seven, the skin splitting along the back and the insects coming out 

 white, soft, but rapidly hardening and 

 assuming the normal color. Some 

 astounding statements have been made 

 as to the length of time required for the 

 development of the roach from the egg to *^^ 

 the adult. Four or five years have been j-,^ ^Egg-capsule of Pen^neta 



said to be necessary for an individual to amencana: a, side; 6, end view. 



reach full grow^th; but more recent breed- fi^re'^^^^orTginTio'^'^'''* ^^ outi'ne 

 ing experiments have not altogether con- 

 firmed these statements. Their development, however, is unquestion- 

 ably slow, and probably under the most favorable conditions rarely is 

 more than one generation per year produced. In colder countries the 

 breeding and growth are practically restricted to the warm season. 

 During the winter months they go into concealment and partial hiber- 

 nation. BlatteJla germanica has been shown to reach full growth in a 

 variable period of from four and a half to six months (Hummel, Essais 

 Entomologiques, No. 1, St. Petersburg, 1821). The common Ameri- 

 can roach (Periplaneta americana) has been carried from the egg to 

 the adult state in our insectary. Young hatching July 1 1 from an egg 

 case received from Eagle Pass, Tex., reached the adult stage between 

 March 14 and June 12 of the following year, indicating a period of 

 nearly twelve months for comj)lete development. The rate of growth 

 of the roach undoubtedly depends very largely on food and tempera- 

 ture, and under unfavorable conditions the time required for develop- 

 ment may undoul)tedly be vastly lengthene<L The abunchince of 

 roaches is, therefore, apparently not accounted for so much by their 

 rapidity of multiplication as by their unusual ability to preserve them- 

 selves from ordinary means of destruction and by the scarcity of 

 natural enemies. 



THE COMMON DOMESTIC ROACHES. 



The four roaches which have been made the subject of illustrations 

 represent the species which occur most commonly in houses, bakeries, 



[Clr. 51] 



