To solve this problem, we need to understand the anatomical structure of a cockroach's body.$\newline$The body of a cockroach is divided into three main parts: head, thorax, and abdomen. Each segment of these parts is covered by hardened plates.$\newline \bullet$Terga (singular: tergum) are the dorsal plates.$\newline \bullet$Sterna (singular: sternum) are the ventral plates.$\newline \bullet$Pleura (singular: pleuron) are the lateral plates.$\newline$These plates are not directly fused together; instead, they are joined by a flexible membrane.$\newline$This flexible membrane is known as the arthrodial membrane.$\newline$The arthrodial membrane allows for movement and flexibility between the segments.$\newline$Now, let's analyze the options:$\newline \bullet$Option 1: Cementing glue - This is not applicable as the segments are not glued together.$\newline \bullet$Option 2: Muscular tissue - While muscles are present, they do not join the terga, sterna, and pleura.$\newline \bullet$Option 3: Arthrodial membrane - This is the correct answer as it is the flexible membrane that joins these plates.$\newline \bullet$Option 4: Cartilage - Cockroaches do not have cartilage; this is found in vertebrates.$\newline$Therefore, the correct option is Option 3: Arthrodial membrane.