September 28, 1883.] 



SCIENCE. 



431 



upon. The long momoir embodies a laige number 

 of valuable data, the outcome of work which we 

 believe to be thorough and careful. The collation 

 of the literature is good, but not complete, some 

 omissions being important. We are unable to give 

 here more than the chief general conclusions. 



The skin of the larvae studied consists of a single 

 layer of large flattened cells, covered externally by 

 the hard chitinous cuticula (containing lime in 

 Stratiomys), which is smooth in Musca and Eristalis, 

 but divided in Stratiomys into fields corresponding 

 to the cells. Below the cells, and lying directly 

 against them, is a thin anhistic membrane, which is 

 comparable to the basal membrane in Crustacea and 

 adult insects. 



The peripheral nervous system is of great interest. 

 Between the integuments and the muscles of the 

 larvae are found peripheral ganglia, which do not 

 belong either to the ventral chain or to the stomato- 

 gastric system. No analogous observation has hither- 

 to been made upon insects. The peripheral ganglia 

 of the larva of Tipula are very remarkable from 

 their regular disposition and their symmetry: there 

 is a pair in each segment. Those of Musca are 

 irregularly scattered between the sldn anil the 

 muscles. Analogous ganglia are found in Eristalis, 

 but are localized in the plexus, whence spring the 

 nerves of the special sense-organs in the anterior 

 region of the body. In the description of the pe- 

 ripheral nerves the author adds little to what was 

 previously known. 



The sensory nerves end in two ways, — either by 

 a connection with sensory hairs of the epidermis, or 

 with free terminations. In the former case the axis- 

 cylinder dilates, at the base of the sensory hair, into 

 a bi-polar ganglion cell. The sensory hair is a 

 conical hollow process of the cuticula. It is secreted 

 by a special, large, slightly modified epidermal cell, 

 the protoplasm of which tills the cavity of the hair, 

 and lines its base. The distal prolongation of the 

 bi-polar cells unites with the protoplasm of the hair- 

 cell, and does not run directly to the hair. This 

 ai)paratus appears to subserve touch, smell, etc. 

 The free terminations are found beneath the epider- 

 mis, as thread-like prolongations of a very rich dermal 

 plexus, formed by very numerous multi-polar anas- 

 tomosing nervous cells. (Besides the description of 

 similar structures in other animals cited by Viallanes, 

 qf. Canini and Gaule, Science, ii. 279.) 



Involuntary striated muscles. The larval heart 

 is histologically comparable to a vertebrate capillary, 

 being formed of fiat cells soldered border to border. 

 In the protoplasm of these cells, muscular fibres are 

 formed, so that the cells are at once comparable to 

 the endotheliiun and muscularis of the capillary. 

 Within each single cell tlie fibrilla begins and ends 

 with a thin disk or stria; therefore the space between 

 the two disks is the unit of the fibril. In young 

 larvae the heart is a .simple tube without lateral 

 openings. The striated muscles of the digestive 

 tube are probably histologically identical with those 

 of the heart, i.e., modified single cells; but Viallanes 

 was unable to make out the cell-limits. In the walls 



of the stomach of Tipula is an intramuscular gan- 

 glionated nerve-plexus, which probably innervates the 

 muscles; but the final terminations were not seen. 

 This is regarded .as confirmatory of Ranvier's law 

 {Ler. d'anat. (jinir., 1880, 403). 



In regard to the voluntary muscles the following 

 conclusions are drawn: the fibriUae of insects are 

 homologous with those of vertebrates, although the 

 latter are indivisible, while in insects certain fibriUae 

 (of the wing-muscles) may be decomposed into fi- 

 briculae. In insects, as in vertebrates, the fibriUae 

 are united into ' colonettes,' or little clusters, being 

 closely cemented together by a homogeneous and 

 continuous substance, into which neither protoplasm 

 nor nuclei ever penetrate. In vertebrates a large 

 number of colonettes are united within a com- 

 mon envelope, the sarcolemma, to form the fibre or 

 primitive bundle. In insect larvae this disposition is 

 maintained, but in the wing-muscles the sarcolemma 

 is absent; the primitive bundle then consists of a 

 few colonettes (ilusca), or even of one colonette only 

 (c/. Ciaccio, Science, i. 247, whose paper is not 

 cited). In the leg-muscles there is but a single 

 colonette in each fibre, and the sarcolemma is scarcely 

 developed. As regards the motor plates the follow- 

 ing points are noted : 1°. In the larva of Stratiomys 

 chamaeleon, each of the fibres, constructed on the 

 vertebrate type, has several Doyere's cones, to the 

 summit of each of which runs an axis-cylinder ac- 

 companied by a nucleated sheath. Before innervat- 

 ing the muscle, the nerves form a plexus; in the cone 

 the axis-cylinder forms a terminal arborization 

 by successive dichotomous branchings inside the 

 saroolemma; the fundamental substance contains 

 neither granular matter nor nuclei. 2°. In Tipula 

 there is a similar arrangement, but only one cone to 

 each fibre; the terminal arborization is much more 

 extended, and bears nuclei ; and the basal substance 

 of the cone is granular, and nucleated as in the 

 terminal plates of Amniota. 3°. In the caudal mus- 

 cles of Eristalis and the leg-muscles of Dytiscus, 

 e.ach fibre of which contains only a single colonette, 

 the motor nerves form no arborization, but break up 

 into their constituent fibrils as- soon as they reach 

 the sarcolemma. 



The second part of the memoir deals with the 

 very remarkable changes in the larval tissues at 

 pupation. The corpuscles of the blood of the larva 

 are embryonic cells analogous to the leucocytes of 

 vertebrates, and are foimd in the same form in the 

 pupae. The muscular fibres of the larva disappear 

 at the commencement of pupal life, and in two ways : 

 — First, by ' Evolution rdgressive : ' the nuclei of the 

 muscle become spherical, and each surrounded by a 

 coat of protoplasm, thus becoming, a muscle-cor- 

 puscle, which proliferates, and gives rise to a great 

 number of rose-colored granules, which multiply 

 until the muscular substance entirely disappears, as 

 if it supplied nutriment to the granules; these last 

 finally separate, and spread themselves through the 

 body cavity. Second, by degeneration: the nuclei 

 keep becoming rarer until they all disappear, and 

 meanwhile the contractile substance disappears as if 



