586 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the ceplialothorax in the space between the first and second pairs of feet ; 

 they are situated, however, very much higher than the feet, and there are 

 no signs of them in the adult. It is difficult to say what these provisional 

 organs mean, but they may perhaps be best compared with the paired 

 appendages found, in the embryo of Asellus. In Galeodes they are invested 

 in a distinct cellular layer, which is altogether identical with the matrix of 

 the general body-covering, but which does not contain tracheas, nerves, or 

 muscles. 



As there was not, in the stage observed, any indication beneath the 

 cuticle of the various appendages which are permanently connected with 

 the skin, it is probable that the Galeodidse live for a time in this pupal 

 condition after escaping from the egg. 



e. Crustacea. 



Parasitic Castration and its influence on the External Characters of 

 male Decapod Crustacea.* — Prof. A. Giard has found that Sacculina 

 Fraissei, which is parasitic on StenorJiyncJius phalangium, so acts on the 

 males as to give them very much the appearance of females ; indeed, if one 

 neglects to lift the caudal appendage and observe the position of the genital 

 orifice there is some difficulty in determining the sex. Similar modifica- 

 tions were observed with young males of Portunus Tiolsatus infested by 

 Sacculina Andersonii (sp. nov.), and less considerable modifications were 

 detected in other species. The Bopyridse which infest young Decapods 

 bring about similar results, and Perez has noticed a case of parasitic 

 castration in the hymenopterous insects of the genus Andrena which is in- 

 fested by Stylops. The author discusses the results arrived at, and comes 

 to the conclusion that the modifications due to parasitic castration must be 

 assimilated to those which are the result of progenesis — progenesis obtain- 

 ing when sexual reproduction occurs in a more or less precocious manner, 

 the products being matured before the creature has attained its full 

 development. 



In addition to their intrinsic interest the observations of Prof. G-iard 

 have an important bearing on the question of the value of the older statistics 

 with regard to the Ehizocephala ; the date of fixation of the parasite may 

 be approximately fixed by the knowledge of the fact that the modification of 

 the external sexual characters is the result of the profound lesion of the 

 genital glands. The fact that a parasite provokes in its host an abnormal 

 development of organs which protect it at the expense of its victim seems at 

 first sight very exceptional, but it is to be regarded as a mutual adaptation 

 which is not without analogy with numerous facts of symbiosis, w^hile the 

 deformations produced in various plants by the Cecidomyiae or the Cynipidae 

 are phenomena of exactly the same kind ; a curious case is that of the 

 white campion (Melandryum album') which is infested by TJstilago 

 antJierarum ; when the parasitic fungus is developed on a male plant it 

 fructifies in the stamens, when it falls on a female the stamens, instead of 

 remaining rudimentary, become completely developed just as the male 

 StenorJiyncJius widens its abdomen to protect the Sacculina Fraissei. 



Palsemonetes varians.f — M. T. Barrels gives a careful account of the 

 characters of Palsemonetes varians Leach, and discusses its geographical 

 distribution. As to the somewhat anomalous characters of the latter the 

 following explanation is offered ; in earlier times the ancestors of existing 



* Bull. Sci. Dep. Nord, x. (1887). Cf. Ann. and Mag. Nat. Hist., xix. (1887) 

 pp. 325-45. 



t Bull. Soc. Zool. France, xi. (1887) pp. 691-707 (1 pi.). 



