No. I.] CONTRIBUTION TO INSECT EMBRYOLOGY. 1 27 



they arise, if his account is correct, before metameres are 

 established. It is only on the supposition that the germ-cells 

 of Blatta are precociously segregated that their method of 

 origin can be satisfactorily compared with the conditions seen 

 in Annelids, for in this group the germ-cells are not differ- 

 entiated—so far as I am aware — until after the somites have 

 reached a considerable degree of development. Providing, 

 therefore, that I have not overlooked the germ-cells in precoelo- 

 mic stages, Xiphidiiim must be regarded as presenting more 

 primitive conditions than Blatta. 



In Xiphidmvi and Blatta six, and therefore more than half 

 the total number of abdominal segments, produce germ-cells.^ 

 In one case I found well-developed clusters in the tenth 

 segment, so that if we omit the eleventh or telson-segment, 

 which is rudimental and hence cannot be expected to produce 

 germ-cells, and if, moreover, Heymons is correct in stating that 

 reproductive elements occur in the seventh, only two abdominal 

 segments fail to produce germ-cells ! This consideration lends 

 support to Heymons' suggestion that " iirsprunglich die Sexual- 

 zellen auch in den hinteren Segmenten des Abdomens noch in 

 derselben typischen Weise auftraten." The resemblance of 

 the insect-embryo to Annelids in which a great number 

 of consecutive segments produce ova and spermatozoa, is very 

 obvious. The high development of the appendages and their 

 musculature in the thoracic and oral segments of insects per- 

 haps sufficiently accounts for the complete elimination of the 

 germ-cell clusters in these regions. It may also be noted that 

 they are normally absent in the abdomen in the very segments 

 which longest retain traces of quondam ambulatory append- 

 ages — viz. the eighth to the eleventh. 



The indications of metamerism which are so transitory in 

 the sexual Anlage of the Orthoptera would appear to be retained 

 throughout life in some of the Thysanura. In lapyx, according 

 to Grassi ('89), the arrangement of the egg-tubes is "nettement 

 metamerique," and his Fig. 44, PI- IV, represents in either 

 ovary seven egg-tubes, occurring in consecutive abdominal seg- 



1 In a single instance (Fig. 55, PI. VI) what I took to be a sexual cell was 

 found in one of the coelomic cavities of the metathoracic segment ! 



