Larva of Pseudomyrma gracilis. A, ventral; B, lateral view; C, head and adjacent portions of same enlarged; D, sagittal section through anterior portion of larva. o, oral orifice; x, exudatoria; t, trophothylax, or pocket, which holds the pellet; (pe), deposited by the worker nurses and which is eaten by the larva. Note the hooked dorsal hairs of the larva, which serve to suspend it from the walls of the nest. a, mouth cavity, more enlarged to show the fine spinules (also seen in C), which serve to triturate the pellet and probably also as a stridulatory organ. Vol. XV.-26. A, ventral; B, lateral view of the first larval stage ("trophidium") of the Ethiopian Pachysima latifrons, showing the peculiar appendages ("exudatoria") surrounding the head. These belong to the three thoracic and the first abdominal segments. segments, and the first abdominal segment, which lies immediately behind the head, has in the midventral line a singular pocket, the trophothylax (t). Furthermore, each side of this segment and each ventrolateral portion of the several thoracic segments is developed as a peculiar protuberance or appendage, which functions as a blood-gland, or exudatorium (x). Unlike the adult ants the larvæ can devour solid food, though they are often fed, at least in their youngest stages, with liquids regurgitated on their mouths by the worker nurses. The larvæ of the Pseudomyrminæ are fed with the pellets (pe) from the infrabuccal pocket, which are placed by the workers in the trophothylax where they are within easy reach of the mandibles and can be gradually drawn into the mouth, triturated and swallowed. Some primitive ants (Ponerinæ, some Myrmicinæ, etc.) actually feed their young with pieces of insects or entire small insects, which are simply placed on the ventral surface of the larva within reach of its mouth-parts. In a former lecture I referred to the fact that the larvæ of the social wasps, either before or after feeding, produce droplets of a sweet salivary secretion, which are eagerly imbibed by the adult wasps, and I designated this interchange of food between adult and larva as trophallaxis. I have recently made some observations which show that the ant larvæ also produce secretions which appeal to the appetites of their nurses. These secretions are more varied than in the wasps. Certain ant larvæ undoubtedly supply their nurses with saliva, but many or all sweat a fatty secretion through the delicate general integument of the body, and the larval Pseudomyrminæ produce similar exudates from the papillæ or appendages above described. Although these various substances are produced in very small quantities they are of such qualities that they are eagerly sought by the adult ants. This explains much of the behavior which has been attributed to maternal affection on the part of the queen and the workers, such as the continual licking and fondling of the larvæ, the ferocity with which they are defended and the solicitude with which they are removed when the nest is disturbed. In other words, a decidedly egoistic appetite, and not a purely altruistic maternal anxiety for the welfare of the young constitutes the potent "drive" that initiates and sustains the intimate relations of the adult ants to the larvæ, just as the mutual regurgitation of food initiates and sustains the similar relations among the adult workers themselves. I am convinced that trophallaxis will prove to be the key to an understanding not only of the behavior I have briefly outlined Second, third and fourth (adult) larval stages of Pachysima latifrons, showing the gradual dwindling of the exudatoria. A and B show the trophothylax (t); and B also shows the food pellet pe; which is the pellet formed in the infrabuccal pocket of the worker nurse; r, exudatorium. See Figs. 62 and 63. but also of the relations which ants have acquired to many kinds of alien organisms. In the accompanying diagram (Fig. 65) I have endeavored to indicate how trophallaxis, originally developed as a mutual trophic relation between the queen ant and her brood, has expanded with the growth of the colony, like an ever-widening vortex, till it involves, first, all the adults as well as the brood Trophic Relations Trophic Relations Trophallaxis between Ants of Different Species. trophallaxis between Ants and True Guests. Trophallaxis between Adult Ants. Trophallaxis between Mother or Adult Workers and Larval Brood. Mutual Regurgi- Symphity Social Parasitism Trophobicsis Phylophily FIG. 65 See text for explanation. and therefore the entire colony; second, a great number of alien insects that have managed to get a foot-hold in the nest as scavengers, predators and parasites (symphiles); third, alien social insects, that is, other species of ants (social parasites); fourth alien insects that live outside the nest and are "milked" by the ants (trophobionts), and fifth, certain plants that are regularly visited or even inhabited by the ants (myrmecophytes). These extranidal relationships, represented by the two outer rings in the diagram are, of course, incomplete or one-sided, since the organisms which they represent are not fed but merely cared for or protected by the ants. In my next lecture I shall have more to say about some of these relationships. (To be continued) WATER1 By Professor LAWRENCE J. HENDERSON HARVARD MEDICAL SCHOOL HE task of science is one that may be fulfilled quite directly a by providing useful information of a practical sort for our immediate needs, or it may furnish us with general ideas which, if we are skilful enough and intelligent enough, we may use to explain a great variety of phenomena. These general ideas when combined make up our conception of the universe. The latter function of science is the more important one. It is the one that brings science close to philosophy. It is the one that arouses the greatest interest and enthusiasm in those who pursue the task of science. When we look for generalizations of this kind we always seek simple explanations of nature, confident that they may be used as guides to our action in particular cases and as means for gaining an ever increasing control of the world that we live in. Everything in the history of science justifies us in saying that it is the general interpretation of nature which, especially in the last hundred years, has given man his extraordinary increase in material power, an increase in power which he has used far from wisely no doubt, but which for better or for worse he possesses. In the ancient world there were a certain number of advances of this kind. The history of geometry, in spite of the labors of the last century and in spite of Einstein, is to a great extent ancient history. The few necessary general conceptions that the Greeks found out enabled them to develop a complete science of geometry, enabled them to be good surveyors, enabled them to begin to understand how to lay out the heavens and the earth in their astronomy and in their geography, enabled them to see how to make buildings, and to do a great many practical things. But in the main the really important, the really general ideas of science, are modern, and of course the most interesting ones have to do, at least so most people will think, not with statie things, not with space taken by itself, but with dynamic things, with the question of what is happening in the world. On the whole, the most interesting and the most important generalizations of science 1 This lecture was one of the public series given in Boston on Sunday afternoons recently under the auspices of the Harvard Medical School. |