214 ENTOZOA. 



latter, there are layers of longitudinal and transverse muscular 

 fibres, pervaded by a great quantity of so-called calcareous corpus- 

 cles. These oval bodies, about which more will be said hereafter, 

 also occur in the corium, but not in the cuticular layer. Beneath 

 these structures, in the mature segments, we find a dense layer of 

 parenchyma, which forms a Hmiting membrane, within which is 

 enclosed the central reproductive mass. This latter consists of an 

 anterior testicular group of elements, and a posterior uterine group. 

 The former, in place of a simple testis, consists of a number of 

 small vesicles or sacs, in which filiform spermatozoa have been 

 detected ; these latter, when ripe, being conducted by a vas deferens 

 into a seminal pouch from which a canal passes laterally into the 

 penis; the latter organ, in its retracted condition, being lodged within 

 a flask-shaped sheath or cirrhus-pouch. The female organs are some- 

 what more comphcated. They consist of two masses of viteUigene 

 glands occiipying a limited space, a small ovarium, a centraUy- 

 placed and largely-developed branched uterus, canals of outlet lead- 

 ing from all these organs, and enlargements of the main passages 

 to form internal seminal reservoirs ; also, a vaginal canal, which 

 is widened at its termination to form a receptaculum for the curved 

 penis. These several parts, as weU as their development, have been 

 ably determined and investigated by Leuckart, to whose well-known 

 treatise I must refer those who desire more minute details. 



In addition to the above-named structures, the entire series of 

 joints ff om the head downwards are traversed by a set of vascular 

 canals, which are doubled in the region of the head. These consti- 

 tute the so-called aquiferous system. It is usually described as 

 consisting of two main channels, one passing down on either side 

 of the worm, and both being connected by transverse vessels, which 

 occur singly at one end of every joint. This statement of their 

 arrangement is substantially correct ; and without entering into 

 minute details, I may here remark, in passing, that they do not 

 form tubes of uniform thickness throughout their course, but pre- 

 sent distinct bulbous enlargements at every joiat, where the trans- 



