ON THE STRUCTURE OF THE MALPIGHIAN BODIES 295 



fore, only represented those fragments of the capillary network in 

 which blood corpuscles were clearly distinguishable, their colouring 

 matter being retained by the syrup. After the addition of water, it is 

 often impossible to recognize the capillaries at all ; but using syrup, I 

 have readily enough seen them in all the animals above mentioned. 



It may then perhaps be fairly concluded that, in mammals, the 

 Malpighian bodies are traversed by minute arteries, and contain, in 

 addition, a network of capillaries. 



2. The Structure of the " Contents" or Pulp of the Malpighian Bodies. 



Almost all writers have agreed in stating that the interior of the 

 Malpighian bodies is filled by a liquid, consisting, as Kolliker says, of 

 a small quantity of fluid with a large proportion of corpuscles. How- 

 ever, I have been quite unable to convince myself of the existence of 

 any fluid matter at all in the interior of the perfectly-fresh Malpighian 

 bodies of any of the animals I have examined. On the other hand, 

 the Malpighian pulp appears to me to be as solid as any other 

 indifferent tissue, e.g., that which constitutes the lowest layer of an 

 epidermis or epithelium, or as the most superficial portion of any 

 dermal structure. It is, indeed, like these, soft and capable of being 

 crushed into a semifluid substance, which becomes diffused in any 

 surrounding liquid, like mud in water ; but that it is a soft solid and 

 not a fluid, results, I think, from what I have stated with regard to 

 the difficulty of completely detaching it from the arterial twigs. 



The essential structure of the Malpighian pulp appears to me to 

 be that of every other indifferent tissue which I have yet examined ; 

 it consists, in fact, of a homogeneous, transparent, structureless matrix, 

 or periplast, containing closely-set rounded or polygonal vesicular 

 endoplasts : these vary in diameter from less than i -5000th inch up 

 to I -2500th, or a little more, and contain usually one to three, but 

 frequently many, minute granules ^ (fig. 4). On the addition of acetic 

 acid, the periplast often becomes granular and less transparent, while 

 the endoplasts are rendered darker and more sharply defined, under- 

 going a certain wrinkling. There are neither cell cavities nor cell 

 walls distinguishable around these endoplasts, and therefore the Mal- 

 pighian pulp cannot be said to be composed of ' nucleated cells ; '' 



1 These therefore correspond with the " nuclei " and " nucleoli " of authors. The reasons 

 for not so denominating them are contained in an article 'On the Cell Theory' {'Brit, and 

 For. Med. Chir. Review, October 1853'). I may observe that I know of no tissue better 

 calculated to illustrate the view which I have there taken of Histogenesis, than the Malpig- 

 hian pulp. 



