ASCARIS LUMBRICOIDES LINN.EUS 8 1 



homogeneous layer is the thickest, equal to or even exceeding in 

 thickness all other layers taken together. The cuticle is non- 

 porous : and transversely plicated. Under the cuticle is a thin 

 syncitial subcuticle containing nuclei. The cuticle is a product 

 of this layer which may be best termed hypodermic. 2 Under the 

 latter is a single layer of longitudinal muscles. Each muscle cell 

 consists of a protoplasmic core or cell body and a contractile sheath. 

 The protoplasm is highly vacuolated. It contains the nucleus 

 and a system of supporting fibres. The contractile sheath is 

 drawn out on one side of the cell into a flat spindle which is 

 longer than the cell body and is differentiated into longitudinal 

 fibres. In a cross-section the fibres appear therefore arranged in 

 two rows, at first parallel and barely separated from each other, 

 then diverging and partly inclosing the protoplasmic core. The 

 fibres are inserted directly into the cuticle. The protoplasmic 

 core with its supporting fibrillae sends out processes to the nerves 

 in the longitudinal lines. The layer of longitudinal muscles is 

 divided by these lines into four longitudinal fields or bands. 

 In some Nematodes there are only two muscle cells in a cross- 

 section of a band. But in Ascaris there are several muscle cells 

 to a cross-section of a band and Ascaris belongs therefore to the 

 so-called polymiaria. 



Body cavity. Ascaris has no true body cavity. The 

 cavity which one sees in dissecting the worm is in reality a sys- 

 tem of intracellular spaces, or large vacuoles in a few enormous 

 cells which fill out the space between the longitudinal muscles 

 and the alimentary canal and reproductive organs. The vacuoles 

 are so large and so many that the walls between them are quite 

 thin and have been overlooked until recently. Ascaris and 

 with it all other Nematodes shows more relation to the 



1 What has been described as a system of minute canals proved to be the 

 fibrillar layer. 



2 The subcuticle is usually called ectoderm. The term hypodermis, 

 first proposed for a similar layer in Arthropods, is less confusing since there 

 are in Ascaris other organs of ectodermal origin. 



