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This view has also been held by Carrière and Cholodkowsky, but Heymons concludes from his embryological studies on Forficula and Blattidæ (1895) that it is unfounded. That this is probably the case is proved by the fact that the apodemes of the thoracic region are evidently not modified tracheæ, since the stigmata and tracheæ are present.

Number of segments in the head.

These discordant views were based on the examination of the head in adult insects; but if we confine ourselves to the imago alone, it is impossible to arrive at a solution of the problem.

Newport took a step in the right direction when he wrote: “It is only by comparing the distinctly indicated parts of the head in the perfect insect with similar ones in the larva that we can hope to ascertain the exact number of segments of which it is composed.” He then states that in the head of Hydroüs piceus are the remains of four segments, though still in the next paragraph, when speaking of the head as a whole, he considers it as the first segment, “while,” he adds, “the aggregation of segments of which it is composed we shall designate individually subsegments.”