STUDIES IN THE EXI'EKIMENTAL ANALYSJS OF SEX. 229 



to tlie abdotninal appendage of an iufected female, in which 

 the endopodites are veiy frequently thus reduced. 



We have now examined in some detail two of the most im- 

 portant cliaracters in which the infected male Inachus is 

 modified by the presence of the pai-asite Sacculina, viz. the 

 shape of the abdomen and the form of the abdominal appen- 

 dages, and we have seen that Professor Morgan's attempt to 

 explain the modiKcation of tiie male as a return to a 

 juvenile condition is quite at variance with the facts. But 

 we have still two more points to considei-, which render that 

 explanation still more impossible. 



The most important of these two points is the fact that in 

 a certain small percentage of cases the infected males, on 

 recovery from the parasitic disease, have been observed to 

 have regenerated the gonad, and to have developed large ova 

 measuring about 1 mm. in diameter and full of the reddish- 

 coloured yolk characteristic of the mature ova of the female 

 Inachus. Professor Morgan himself admits the cogency of 

 this fact, so that I neeil not labour it here, its significance, 

 indeed, being obvious. 



The second point is one which I have only been able to 

 settle final 1}' during my recent visit to Naples. In my earlier 

 work (loc. cit., p. 68) I inclined to the view tliat the presence 

 of Sacculina caused the young females under 18 mm. in 

 carapace length to assume prematurely the adult type of 

 abdomen and abdominal appendage, and I emphasised this 

 point as being of importance in precluding the view that the 

 effect of the parasite was merely to arrest development or 

 cause u leturn to a juvenile state. By a careful examination 

 of the large amount of material put at my disposal by Dr. 

 Lo Bianco this winter, I have found that this premature 

 assumption of adult characters by infected females undoubtedly 

 occurs. During December and January all the uninfected 

 females of carapace length up to 14 mm. had the immature 

 juvenile form of abdomen and appendage, but all the infected 

 females measuring from 6-14 mm. had the fully adult type of 

 both those structures. The real theoretical significance of 



