432 



SCIENCE. 



[Vol. II., No. 34. 



dissolved away on the outside. In consequence of 

 these processes, the body cavity is charged with a 

 quantity of matter resembling the vitelline elements 

 of birds. The cells of the so-called fat-body produce, 

 during the first days of pupal life, numerous granules, 

 which enlarge, and are ultimately set free by the 

 rupture of the cell-membrane. These granules arise 

 independently of the nucleus, but closely resemble 

 small cells. The cells of the tracheae and salivary 

 glands do not disappear at the time of metamorphosis, 

 as has been thought, but, on the contrary, they pro- 

 liferate by endogenous cell-formation, the parent 

 cell being first enlarged; the parent nucleus is finally 

 discharged ; the embryonic cells thus generated sep- 

 arate, and fall into the general body cavity. The 

 komchenkugel produced by pupal histolysis, and 

 described by Weissmann, are of two kinds, and do not 

 arise from the disintegrated matter, as supposed ; but 

 the smaller are derived from the muscle-corpuscles, 

 the larger from cells of the fat-body. The epidermis 

 of the larval head and thorax dries up and falls off. 

 It is not immediately replaced by the definite cell- 

 layer, but first by a thin cuticle, which Viallanes 

 considers to be probably the thickened basement 

 membrane of the larva. 



Part third treats of the histogenesis of the tissues 

 of the imago. The skin of the head and thorax is 

 developed from Weissmann's imaginal disks. In the 

 description of these, Viallanes follows Ganin in 

 general, but he thinks that the mesoderm of the 

 disks is formed at the expense of some of the embry- 

 onic cells in the body cavity. Other points are also 

 brought forward, among which we note especially 

 that the wing of the pupa contains at first numerous 

 tracheae, which disappear before the end of the 

 stage. In the abdomen, also, there are imaginal disks, 

 four in each segment, and formed by local thicken- 

 ings of the epidermis ; all other parts of the epidermis 

 or hypoderm degenerate, and are resorbed. The 

 disks form two layers, the outer making the new 

 epidermis, and the inner the mesoderm; the disks 

 grow at their borders until they everywhere meet, 

 and form a continuous tissue. The method of re- 

 generation is the same as in the thorax, except 

 that the disks are developed later: the difference 

 assumed by Weissraann and Ganin is not real. The 

 author compares the imaginal disks with the plates 

 in Pilidium. 



The internal muscular mass of the thorax is derived 

 from a single anlage, composed of little cells embedded 

 in a small amount of homogeneous basal substance. 

 This anlage then separates into six cords, corre- 

 sponding to the definite muscles; these grow by 

 peripheral accretion; the muscular substance is then 

 differentiated around the cells, which are disposed 

 with great regularity in the midst of the colonettes, 

 becoming, in fact, the muscle-corpuscles (the neces- 

 sity of omitting a fuller account is much regretted. — 

 Hep. ). The muscles of the legs are derived from the 

 mesoderm of the imaginal disks; the general process 

 of their histogenesis, despite many interesting differ- 

 ences, is the same as that of the wing-muscles. The 

 author makes an excellent comparison between the 



unicellular muscles (heart, stomach) and the pleuri- 

 cellular (wings, legs), or, as we might name them, the 

 mesenchymal and myothelial muscles. 



Nearly a fifth of the entire memoir is devoted to 

 the development of the eye. The brief resume (p. 

 302-305) is the most succinct and perfect account of 

 the structure of the compound eye with which we 

 are acquainted. In the first section the structure of 

 the developed eye of the pupa, before it becomes 

 pigmented, is described. The following is the au- 

 thor's table of the parts of the visual apparatus: — 



CEil compoee 



Lame ganglionnaire 



r Cornee k facettes. 

 J Couche dee cellules crietallln 

 '1 Couche des r^tinules ou reti 

 l.Limilante posterieure de I'a 

 Couche des fibres post-retiDieDnes. 



f Limitante aoterleure de la lame ganglion- 

 naire. 

 Couche des cellules ganglionnairee. 

 Couche des fibres en palissade. 

 Liraitaute moyenne de la lame ganglion- 



Couche des fibres nucl^es. 

 Liraitante posterieure de la lame gauglion- 

 nalre. 

 Couche des fibres pr^ganglionnaires. 



INevrilemme. 

 Couche des cellules en chapelets. 

 Croissant du noyau central, 

 fiventail du noyau central, 

 ficorce grise du ganglion optique. 



Concerning the development of the eye, we give 

 the following conclusions. In the larva, before met^ 

 amorphosis, the eye is represented by three parts, — 

 the imaginal disk of the eye proper, the neural stem, 

 and the optic ganglion. The disk of the eye com- 

 prises the same three layers as the other imaginal 

 disks. Before the metamorphosis of the larva, the 

 superficial cells of the exodermic layer become en- 

 larged and elongated, and acquire a strong alfinity 

 for coloring-matters; they are the optogenic cells. 

 This change begins in the centre, and spreads to- 

 wards the periphery of the disk. The mesoderm of 

 the disk of the eye, unlike the other two layers, is 

 different from the corresponding portion of other 

 disks, since it is composed of fine nerve-fibrillae 

 mingled with nuclei; by teasing, it can be shown that 

 each fibril is connected with the inner end of an 

 exoderm cell. The nervous stem unites the disk of 

 the eye with the optic ganglion, and is composed 

 of the nerve-fibrils mingled with nuclei. The optic 

 ganglion is constituted by the outer portion of the 

 brain; its nucleus consists of white, its cortex of 

 gray, matter; in the lateral portion of the cortex, is 

 the complex anlage of the lame ganglionnaire, in 

 which all the principal constituent parts of the 

 definite lame ganglionnaire can be recognized. At 

 the moment of metamorphosis the following phe- 

 nomena occur: the provisory layer of the disk of 

 the eye disappears, the exoderm enlarges, its borders 

 unite with the neighboring disks, its cuticle becomes 

 the faceted cornea, and its optogenic cells each form, 

 by the known process, an elementary eye. The 

 anlage of the lame ganglionnaire emigrates from the 

 optic ganglion, then enlarges, and spreads oxit so as 

 to intervene between the ganglion and the eye. The 



