The Wax Glands of the Cockroach (Blatta Germanica)

Resumido por el autor, E. H. Dusham. Las glhdulas productoras de cera en la cucaracha (Blatta germanica). La hipodermis de 10s insectos ha sido descrita como formada por una sola capa de c6lulas. Una excepcidn se presenta en la pared dorsal del abdomen del macho de la cucaracha (Periplaneta orientalis), cuya hipodermis estd formada por dos o tres capas de c6lulas. El estudio de las paredes del abdomen ha demostrado que en esta especie dicha estructura existe, no solo en las paredes dorsal y ventral del macho, sino tambi6n en las de la hembra. El autor ha encontrado tambi6n una estructura semejante en Blatta germanica. La capa superior estA formada por cklulas hipod6rmicas semejantes a las que existen en otras regiones del cuerpo, en las que existen c6lulas hipodkrmicas tipicas. Las capas m&sprofundas estan formadas por c6lulas mucho mayores, con grandes nficleos vesiculares y citoplasma granuloso. Su aspecto irregular indica su naturaleza glandular, comprobada ademas por el hallazgo de canales pequefios que se extienden a trav6s de la cuticula que recubre a dichas glandulas, la cual presenta pequefios poros en vista superficial, y por medio de 10s cuales la secrecidn sale a la superficie. El analisis de dicha secrecidn, recogida en la cuticula, ha demostrado que esta formada de cera. En Blatta germanica estas glandulas se dis- tinguen por primera vez despues de la primera muda del tegu- mento, en las ninfas de dos dias, en las cuales algunas de las cblulas hipod6rmicas que ocupan ciertas Areas, aumentan de tamaiio y empujando a las c6lulas hipod6rmicas adyacentes dan a la hipodermis el aspecto de una capa poliestratificada. La hipodermis de la cucaracha, por esta causa, no difiere de la de 10s otros insectos. Translation by Dr. Jose Nonidez, Columbia University. AUTHOR'S ABSTRACT OF THIS PAPER ISSUED BY THE RJBLIOQRAPHICSERVICE, NOYEMBER 18 THE WAX GLANDS OF THE COCKROACH (BLATTA GERMANICA) E. H. DUSHAM Department of Entomology, Cornell University ELEVEN FIGURES INTRODUCTION The ability to secrete wax in one form or another is wide- spread among insects, being reported for the Libellulidae of the Odonata ; Notonectidae, Fulgoridae, Cercopidae, Psyllidae, Aphi- didae, Aleyrodidae, and Coccidae of the Hemiptera; Tortricidae and Papilionidae of the Lepidoptera ; Coccinellidae and Cur- culionidae of the Coleoptera; and the Tenthredinidae and Apidae of the Hjmenoptera. That this function should also be found in cockroaches is not surprising, for they are waxy in appearance, feel waxy when handled, and when thrown into water or other fluids float readily as if buoyed up by some oily covering, even after the air has been forced out of the tracheae by pressure: In fact, one of the difficulties encountered in fixing material is to submerge the specimens in fixing fluids, especially when these are used cold. On the other hand, no such difficulty is experienced when hot fluids are used, the hot liquid evidently melting the wax, thus allowing the insects to sink. Moreover, it is a well-known fact that the species in question is usually found in warm, damp places, kspecially in close prox- imity to sweating water pipes, its association with water pipes leading from the Croton Aqueduct in the vicinity of New York City earning for it the popular name of 'Croton bug.' Further- more, references to the literature of this species show that it has been carried for long distances in water mains without drown- 563 564 E. H. DUSHAM ing. That they have been able to live in moist places and also withstand submerging would lead one to suppose that their bodies were protected by some oily or waxy secretion. HISTORICAL The study of the wax glands of the cockroach is bound up in a controversy as to the number of layers in the hypodermis of these insects. In insects in general the body wall is relatively simple, consisting of an outer chitinous covering or cuticula, the hypodermis consisting of a single layer of cells, and the basement membrane, and as such, Miall and Denny described it in their work on the cockroach, in which they stated that the hypodermis consisted of a single layer of flattened cells, resting on a basement mebrane, each cell corresponding to a polygonal area of the overlying cuticula. In 1888, however, E. A. Minchin, while studying certain glands on the dorsal side of the cockroach, found that the hypodermis, at least on the dorsal side of the older stages of the male, consisted of two layers everywhere except in the intersegmental areas where only a single layer was present. In certain places he found that the cells of these layers had the appearance of giant cells with large nuclei, granular contents, and elongate processes. These he interpreted as ganglion cells. He found them scattered over each tergum, especially at the anterior portion of each tergite-that part which is overlapped by the preceding tergite-although they were also scattered throughout the region posterior to this part. Between these so-called ganglion cells he found the ordinary cells of the hypodermis. He therefore concluded that in the cockroach, at least, the hypodermis consisted of an upper layer of cells corresponding to the polygonal areas of the cuticula, and a lower very irregular layer, occasionally forming two layers, whose cells were modified to form nerve cells, and which were probably connected with setae where the terga were exposed. In 1889, Mingazzini made a detailed study of this apparently double-layered hypodermis in order to verify Minchin’s work, WAX GLANDS OF THE COCKROACH 565 examining the dorsal wall of the abdomen of males in different stages of development. He found that the hypodermis was not always made up of two layers of cells as Minchin described, but sometimes showed a single layer of cells, other times two or more layers. In the intersegmental areas, he found a single-layer of cells as Minchin described. Where the muscle bundles were inserted he also found a single layer of cells, modified in the usual way to form the characteristic muscle attachments. In other places the hypodermis consisted of a single layer of cells, usualiy of small size, or of two layers, the upper layer consisting of small cells, the lower one of much larger cells, or of several layers of cells arranged without order. Except for an occasional large cell at the surface among the smaller cells where a singlelayer of cells was present, the majority of the larger cells were below the smaller ones. He concluded that these cells were not to be considered as nerve cells, but as cells of an epithelial nature, derived from the upper layer of the hypodermis, but which had undergone en- largement and were no longer of use in the secretion of the cuticula. He was uncertain whether these large cells were hair- forming cells or gland cells, but because of the structure of the nucleus and protoplasm he favored the glandular view, the insects probably secreting an oily substance. He, therefore, concluded that the hypodermis of the cockroach did not differfrom that of other insects by the nature of the cells which composed it, but only because, as the insects increase in size, many hypo- dermal cells become specialized for a particular function, in- creased in size, took on a branching form, and were carried below the regular hypodermis, thus forming an apparently double- layered hypodermis. In 1909, Berlese, in commenting on this peculiar structure in the cockroach, stated that if the smaller cells were not merely infiltrated amoebocytes, they were to be regarded as a prolifera- tion of the hypodermis, and that possibly the larger cells had assumed another function. At least, he was sure that the con- dition was unique among insects and was still an open question. 566 E. H. DUSHAM LOCATION AND STRUCTURE OF THE GLANDS At the suggestion of Dr. W A. Riley, under whose direction this work was carried out, the writer undertook to settle this question. While the preceding investigations were made on Periplaneta orientalis, yet a study of Blatta germanica showed that similar conditions were present, and because of the abun- dance of the latter, this species was used almost entirely in the following work. In order to show the general distribution of the glands, the abdomen was cut from the anterior part of the body, and a slit through the chitin was made all around its margin, thus sepa- rating the dorsal from the ventral wall. From these respective parts the fat and muscle were removed as carefully as possible so as not to injure the delicate hypodermis. It was found more advisable to fix the entire abdomen before making the incision around the edge, because the greater rigidity after fixation facili- tated cutting, and prevented the parts from curling, as when fresh material was cut. Both dorsal and ventral abdominal walls were then stained with Grenacher’s borax carmine and Delafield’s haematoxylin, and mounted in balsam. Better results were ob- tained with the latter stain. The gland cells are so small that they can hardly be distinguished from the normal hypodermis except for the larger size of their nuclei, and these were rendered more conspicuous by using Delafield’s haematoxylin and destaining with acid alcohol until the nuclei stood out prominently, while the surrounding cytoplasm of the cells was but faintly tinged. The nuclei are even better accentuated by dipping the material in alkaline alcohol after destaining in acid alcohol, as they take on a deep blue coloration after such treatment. As the glands are most prominent at the anterior portion of each segment, and as this portion is covered by the posterior part of the preceding segment, some difficulty was encountered in making out their distribution.

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