728 suiniAKY OF current researches relating to 



In the history of the nervous system we may note the appearance of 

 a pair of cerebral grooves resembling those of Pcripntus ; they become 

 obliterated ami disappear entirely later on. Temporary cavities appear 

 in the ganglia which disappear when the two cords unite to form one ; 

 as to the function of these the author has no suggestion to ofl'er, but ho 

 thinks that the cerebral grooves may be for the aeration of the cerebral 

 tissue, as they disappear as soon as the tracheal invaginations begin to 

 be formed. 



The trachea) arise as pit-like invaginations formed just behind and a 

 little externally to the bases of each pair of appendages ; the walls arc 

 thick and composed of cells like those of the epidermis ; as the pit 

 becomes deeper it forms a kind of vesicle within the body. As this 

 vesicle changes its form it gives off two short thick diverticula ; the cells 

 composing these break up, alter their arrangement, and form the tracheal 

 tubes. The stink-glands also arise as invaginations. 



The heart of the adult Julus, which has never been fully described, 

 has two i)airs of ostia in each segment ; these are originally spaces left 

 in the tubes during development ; the lips of the ostia which project 

 into the tube of the heart are formed by four peculiarly-shaped muscle- 

 cells, which evidently control the operations of the ostium ; there are 

 two pairs of arteries to each segment, and they lead directly into tho 

 spaces of the fat-body. The internal coat of the cardiac tube is not 

 ni;cleated, being secreted by the cells of the middle coat early in 

 development ; this middle coat has a well-developed muscular structure ; 

 the fibres arc circular and disposed in bands, a narrow band alternating 

 with a broad one. The heart is suspended by thin muscle-fibres which 

 are attached to the hypodermic matrix layer; there are also muscle- 

 fibres attached to the fat-body which probably correspond to the alfcform 

 muscles of the heart of insects. The cavity in which the adult heart of 

 Julus is inclosed is partially cut off from the rest of the body-cavity by 

 a pericardial membrane, formed from the same network of cells which 

 gives rise to the heart, and which is continuous with the fat-bodies. 



In the formation of the eye a single ocellus appears first, and tho 

 rest are added on one by one till the full number is reached ; in each 

 case the process of development is the same. A deposition of pigment- 

 granules of a dark red-brown colour takes place within a thickened 

 mass, which has been formed by a multiplication of the cells of the 

 hypoderniis, and this secretion of pigment is accompanied by a separation 

 from one another of certain cells within the mass. As a result, we have 

 the formation of a vesicle bounded by a mass of dark pigment. The 

 cells which compose the external wall of this vesicle give rise to the 

 lens which fuses with the chitin of the exoskeleton, and the same cells 

 continually add layers to the lens till it assumes its full size. This 

 development of the eye-spots from a vesicle agrees with Patten's belief 

 that the simple myriopod eye has been developed from a vesicle 

 invaginated fiom the ectoderm ; but what Patten describes as the 

 vitreous layer is clearly the corneal hypodermis. The original hypo- 

 dermis present before the formation of the eye is represented by the 

 external chitin of the exoskeleton formed by it and now fused with the 

 external wall of the vesicle. 



"With regard to the phjlogeny of the Myriopoda, it is observed that 

 the essential featm-es which they have in common with Peripalus, are 

 such as would be likely to occur in many Tracheata, if the latter are 



