46 EIOHAED EVANS. 



The next stage to be considered is represented by the fifth 

 fio'ure on PL 5. The most marked chang'e that has been 

 effected, as compared with the previous stage (shown in the 

 fourth figure of the same plate), consists in increase in size, 

 the embryo in its folded condition being two and a half 

 times as long as the previous one. The posterior end of 

 the embryo is passiug from the strictly dorsal and median 

 position to the left side of the head preparatory to unfolding 

 itself. When the posterior end has slipped off the back it 

 may become slightly coiled, so as to produce a short spiral, 

 and, owing to both ends of the embryo simultaneously un- 

 twisting themselves in opposite direction, which sometimes 

 happens, the whole body may for a time present the appear- 

 ance of being spirally twisted. The ring-like markings 

 occurring on the body and appendages are gradually becom- 

 ing deeper. 



The sixth figure on PI. 5 illustrates the next stage of 

 development to be studied. In the embryo under considera- 

 tion the posterior end displays a curious twist, which it has 

 acquired in passing from the left side and in becoming ex- 

 tended. The anterior end of the embryo is so placed that 

 the ventral surface is turned towards the right side, but 

 does not slip over to the side as the posterior end does. The 

 flexed anterior end, besides being twisted laterally, is un- 

 folding itself longitudinally; for in the embryo under con- 

 sideration it carries only two pairs of the walking appendages, 

 while in the one described in connection with the previous 

 stage, and illustrated by the fifth figure on PL 5, it was 

 provided with four pairs. The actual length of the embryo 

 in its folded condition was 7 mm. 



The next stage of development to be considered is repre- 

 sented in the seventh figure on PL 5. With the exception 

 of the head, which is bent down towards the ventral sur- 

 face, the body of the embryo has attained the extended 

 condition of the older ones which occur in the uterij and its 

 colour is just beginning to turn brown. Only the first pair 

 of walking- appendages are in any way involved in the 



