1887.] Post-embryonic Development of Julus terrestris. 243 



II. " The Post-embiyonic Development of Julus terrestris." 

 By F. G. Heathcote, M.A. Communicated by Adam 

 Sedgwick, F.R.S. Received November 16, 1887. 



(Abstract.) 



With regard to the development of the ccelom and generative 

 organs, I have obtained the following results. The somites divide 

 into two parts, as described for Strong ylosoma by Metschnikoff, one 

 part remaining in the body and the other part projecting into the 

 legs. The cavities in these two parts together constitute the ccelom. 

 The part within the legs breaks up and the cells give rise to muscles. 

 The part within the body passes dorsalwards along the thin sheet of 

 mesoblast which unites it to its fellow of' the other side, so that the 

 two vesicle-like parts meet above the nerve-cord in the middle line. 

 They join so as to form a single tube, the generative tube. The young 

 ova, as well as the follicle cells surrounding them, are formed by cells 

 proliferated from the walls of this generative tube. The body parts 

 of the somites of the antennas and mandibles break up and disappear, 

 but those of the third pair of appendages give rise to the pair of 

 salivary glands. There are two pairs of somites to each double 

 segment. 



In the development of the nerve-system, I find that there are two 

 cerebral grooves formed as in Peripatus. They disappear early in the 

 development. The ventral nerve-system, which at first consists of 

 two separate cords united by a thin median part, undergoes a process 

 of concentration which results in the presence of a single stout cord 

 showing slight traces of its former double condition. At an early 

 period of development there is a cavity present in each ganglion. 

 This cavity soon disappears, leaving no trace. Two ganglia are 

 developed to each double segment. 



The tracheae are formed as epiblastic invaginations at the sides of 

 and rather behind the legs. These invaginations swell out inside the 

 body so as to form two vesicles, and as the development proceeds two 

 diverticula are given off from each vesicle, one running beneath the 

 nerve-cord to meet its fellow of the other side, the other running 

 dorsally, parallel to the body-wall. Both these diverticula break up 

 to form the tracheal tubes, the remaining part of the vesicle forming 

 the tracheal pit. There are two pairs of these tracheal invaginations 

 to each double segment. 



The stink glands are formed as invaginations of the epiblast, and a 

 second coat (muscular) is added later in the development. There is 

 only one pair to each double segment. 



The heart is formed from mesoblast cells in the body cavity. 



