6 RECORDS OF THE AUSTRALIAN MUSEUM. 



excretory vessels there may be seen in section other accessory 

 longitudinal fibres. There is a ventral and dorsal pair on each 

 side. There are thus ten longitudinal nerves, three pair of large 

 laterals and two pair of smaller cords. 



Musculature, etc. — In transverse sections the cuticle is seen 

 to be rather thin. Below it lie the subcuticular structures con- 

 sisting of very well developed circular muscles and within these 

 the longitudinal fibres. The subcuticular cells are imperfectly 

 preserved. 



The separation between the cortex and medulla is not well 

 marked owing to the poorly developed system of transverse 

 muscle fibres. Lying in the peripheral part of the cortex there 

 was abundance of calcareous corpuscles of an elliptical or rounded 

 form and possessing a diameter of from 0*005 - 0*012 mm. 



The longitudinal muscular system of the parench)*ma is very 

 strongly developed. There are three distinct systems arranged 

 concentrically. The innermost (PI. i , tig. 1, 1. m. 3) is just out side 

 the transverse muscles and is practically restricted to that part 

 of the cortex which lies above and below the female complex. 

 There are here about eight well-marked bundles on each surface, 

 and in addition there are a few isolated bundles lying laterally 

 from the excretory vessels. As these latter occur within the 

 other two systems they probably belong to the same series as 

 those just mentioned. Just externally to this series is the 

 ordinary longitudinal system consisting, as is frequently the 

 case, of an inner (PI. i., fig. 1., 1. m. 2) and an outer (PI. i., fig. 1, 

 1. m. 1) series of bundles. The inner bundles are much larger, as 

 also are the individual fibres, than those belonging to the outer 

 series. The fibres, especially those of the larger bundles, were 

 separated from each other, this being perhaps due to imperfect 

 preservation. These two rings are generally easily distinguishable 

 from each other except laterally where they become more or less 

 merged. Even in the lateral portion of the cortex these bundles 

 are still highly developed. In ripe segments it was noticed that 

 the uterus frequently forced its way dorsally between the longi 

 tudinal bundles so as to lie against the subcuticula and in such 

 cases the uterine lobes might be seen almost surrounding individ- 

 ual bundles (PI. i., fig. 2). At the posterior end of each 

 segment there is seen in sections, a mass of well developed trans- 

 verse muscle. Connecting the dorsal and ventral surfaces there 

 are a great number of strong dorso-ventral fibres. 



Mule Genitalia. — The male glands appear very early and do 

 not persist, but disappear soon after the segment has reached 



