190 Dr. M. Laurie 07i the 



proportion than that of the other forms. In the one specimen 

 in my possession which contains partially developed embryos 

 there appears to be very little, if any, yolk. The embryos 

 develop in the ovarian tube, however, as in Euscorpius. 



In the other type of development * the egg is very minute and 

 contains no yolk. It is placed (fig. 6) at the distal end of a large 

 diverticulum of the ovarian tube, and the embryo as it grows 

 extends down and occupies the cavity of the diverticulum. 

 There appear to be no embryonic membranes, and the embryo 

 is nourished by consuming a solid cord of cells which ter- 

 minates the diverticulum. This type of development I have 

 found in Scorpio, Fleterometrus, Palamnceus, Opisthophthalmus, 

 Opisthocentrus, and Hormurus. Thus, so far as my observa- 

 tions go, it is characteristic of the family Scorpionidfc, but 

 I have not had specimens from the subfamilies Diplocentrini, 

 Hemiscorpiini, or Urodacini. This is the more to be re- 

 gretted as we shall see that there is some reason to doubt the 

 close alliance of, at all events, the Diplocentrini with the other 

 Scorpionidse. 



An additional mode of nourishment of the embryo in the 

 form of two outgrowths from the head, which probably absorb 

 fluid from the surrounding tissues, occurs in Opisthoph- 

 thalmus t- 



A structure which I have not seen fully described, and the 

 function of which is unknown to me, occurs in all the 

 Scorpionidge and Ischnuridfe which I have examined, but 

 seems to be wanting in the Buthidse. It consists of a pair of 

 hollow cylindrical processes projecting back into the abdomen 

 from the posterior side of the diaphragm between the pro- 

 soma and the mesosoma. In sections it is seen to be com- 

 posed of two layers of cells separated by a thick non-cellular 

 layer. The outer cell-layer appears to be continuous with 

 the diaphragm, while the inner one comes into close con- 

 nexion with the capsule of flattened cells surrounding the coxal 

 gland. It is possible that the cavity of this diverticulum is 

 in communication with the lumen of the coxal gland, in w^hich 

 case it is a portion of the coelome. I have not been able to 

 satisfy myself on this point, however. 



III. The Lung-books. 



These are more available for systematic purposes than the 

 preceding structures, as it is possible, by making an incision 



* Laurie, " Development of Scorpio fulvipes,^' Quart. Journ. Micr. Sci. 

 vol. xxxii. 



t Laurie, Proc. Roy. Phys. Soc. Edinburgh, 1895-96. 



