78 NATURAL SCIENCE. August, 



twenty-four hours. Thereafter they sink to the bottom, swim 

 sluggishly for a second period of from twelve to twenty-four hours, 

 and then become fixed, and undergo metamorphosis. The newly- 

 hatched larva is a slightly oval body, the larger anterior pole of which 

 consists of a single layer of ciliated cells, each cell being provided with 

 a single long flagellum. The posterior pole has a smaller number of 

 larger and granular cells. Between the two sets is a zone of inter- 

 mediate cells, which, as Mr. Minchin was able to make out, are 

 transitional stages between the cihated cells and the granular cells. 

 During the free-swimming larval period the granular area gradually 

 increases by transformation of the cells of the intermediate zone, while 

 the intermediate zone grows by transformation of the adjoining ciliated 

 cells. The centre of the larva is occupied by a mass of pigment, and 

 sections showed that this is part of a remarkable larval organ with 

 pigment, a lens-like body, and central granular cells. It is in fact an 

 eye, or rather a light-perceiving organ of a very simple character. 

 This organ apparently is completely thrown out at the metamorphosis. 

 The free-swimming larva fixes itself by its anterior pole. The 

 granular cells grow round the ciliated cells, and the metamorphosis is 

 completed in a few hours. The granular cells become a single super- 

 ficial layer of flattened cells, a layer which Mr. Minchin calls the 

 dermal layer, while the interior is occupied by a solid mass of the 

 original ciliated cells, now called the gastval layer. These two layers 

 develop independently of each other in their subsequent stages, so 

 that in different larvae different stages of the dermal and gastral 

 layers may be associated. This seems to us a point of considerable 

 interest, and one upon which an extended set of observations in all 

 sorts of embryos would be useful. For it seems to bear upon the 

 nature of the process of development, and upon the scope of the 

 intrinsic forces which play at least a large part in the elaboration of 

 an individual. The dermal layer gives rise to an inner layer, the 

 cells of which unite into groups and secrete the triradiate spicules, 

 and an outer layer, each cell of which secretes a single monaxon 

 spicule. A split appears in the gastral mass, and around this the 

 gastral cells become arranged in a single layer, except at one point, 

 the future osculum, at which no gastral cells lie and where the cover- 

 ing of dermal cells ruptures. 



New Mammals from Victoria. 



The discovery of new mammals is so rare an occurrence that 

 we hasten to record Dasytiroides byrnei, n.g. et sp., and SmintJiopsis 

 larapinia, n.sp., two marsupials discovered by the Horn Expedition 

 in Central Australia, and described by Professor Baldwin Spencer in 

 the Proceedings of the Royal Society of Victoria, vol. viii., pp. 5-13, as 

 well as further described and figured in the account of the Horn 

 Expedition. Dasytiroides is a burrowing, insectivorous marsupial of 

 nocturnal habits, which in the general form of the body closely 



