MS DB. H. CHAELTON BASTIAN ON THE ANATOMY AND PHYSIOLOGY 



layer from which the chitinous lamellae are excreted, and which corresponds most likely 

 with what Dr. Cocbold describes as a ' homogeneous' granular layer*. 



As a result of my recent investigations I can now make the following statements. 

 The integument of all the Nematoids examined appeared to be composed essentially of two 

 portions, an external, or ' ecderon,' varying much in different genera, though composed 

 essentially of an uncertain number of layers of a colourless chitinous material, the 

 outermost of which often presented markings, regular or irregular, on its surface ; and an 

 ' enderon,' or internal, active, formative portion, consisting of a cellular layer bounded 

 on both sides by a loose fibrous membrane, uniting it externally with the epidermic 

 layers, and internally with the muscles. In the intermuscular intervals, and especially 

 in the lateral, this layer is much thickened, and projects between the muscles into the 

 general cavity of the body so as to constitute the well-known, though much misunder- 

 stood, ' lateral and median lines' (Plate XXIII. fig. 1), concerning the nature of which so 

 many conflicting statements have been made. The median lines are by no means so 

 common as they seem to have been considered ; in many Nematoids no traces of them 

 exist, and since the lateral lines often contain an axial longitudinal vessel, I shaU defer 

 the further consideration of these developments of the deep cellular layer until I come 

 to speak of the organs of circulation and the so-called ' water-vascular system.' 



I have examined the integument most carefully in Dracunculus medinensis, and also 

 in Ascaris lumbricoides and A. megalocephala, and in these last two animals have found 

 it similar in almost all respects. In them its total thickness, as measured in transverse 

 sections, is about xls" ; rather more than one-fifth of which is due to the thickness of the 

 cellular layer, whilst the remaining portion is made up of the several chitinous lamellae. 

 The distinct recognition of this inner layer as something else than a mere granular mem- 

 brane, and its absolute continuity with the lateral and median lines, is a matter of no 

 small importance for the proper elucidation of Nematoid anatomy ; and this layer also 

 deserves our attention, since it seems to take an active share in the development as well 

 as in the vital functions of these animals. It is not only the formative layer of the thick 

 chitinous envelope, but, in all probability, it takes a most active part in the respiratory 

 processes, since it communicates directly with the exterior, and contains within its 

 substance the principal representatives of the vascular system of the Nematoids. In 

 the Ascarides generally it is well developed, and is distinct also in the Guineawormf 

 and in Spiroptera obtusa, but it was found to be very thin in a species of Filaria and in 

 Prostliecosacter inflexus. 



In transverse sections oi Ascaris lumbricoides or A. megalocephala, the direct continuity 

 and similarity of tissue between this layer and the lateral and median prominences can 

 be easily seen (Plate XXIII. figs. 5 & 16). After a portion of the body has been slit 



• hoc. eit. p. 380. 



t This, -which I was unable satisfactorily to demonstrate before, I have lately been able to make out, together 

 with a few other additional facts, after the examination of some specimens in excellent preservation kindly 

 given to me by Professor Aitken. 



