1. The History and Developnient of Sacculina intema. 47 



with no sign of any roots on the Tower part of the intestine where the adult Sacculina will 

 appear. The histological examination of the youngest of these Sacculinae will disclose the 

 fact that at present no differentiation of organs has appeared, but that the whole body con- 

 sists of a hollow piate drawn out into short processes and composed of a number of large 

 embryonic cells, many of which are undergoing mitosis. With these few directions which 

 doubtless the individuai investigato! will improve as his experience in the matter accumulates, 

 I pass to the description of these youngest stages of ali before the Sacculina has reached its 

 definitive position. Piate 5 fig. 2 represents a young Sacculina interna (sac) on the upper 

 part of the host's intestine, far removed from the definitive position of the adult parasite (#). 



A. Sacculina interna migrans. 



(Piate 5 figs. 1—9.) 



It appears to me probable that when the "embryonic cells" of the Kentrogon have 

 entered the haemocoel of the crab at any point, they are passively carried about until they 

 reach the space surrounding the upper part of the intestine just below the stomach. They 

 then become applied to the intestine in this region and begin to throw out roots and at the 

 sanie time to grow down the intestine towards the definitive position of the adult. Delage 

 supposed that directly after inoculation the cells began to grow and establish roots, the motion 

 of the Sacculina in the crab being from the start purely due to growth. My reason for clis- 

 agreeing with him is that the young Sacculinae internae which I have found attached to the 

 upper portion of the intestine (see Piate 5 figs. 1 and 2) have not exhibited as far as I could 

 observe an elongated root leading to the point of inoculation, and moreover since I have found 

 in every case observed that the Sacculina first becomes attached to the upper part of the 

 intestine and then grows downward, it is difficult to see why, if the Sacculina begins to 

 establish its root system from the first, it should always take this roundabout course to reach 

 its final position near the unpaired diverticulum of the gut. 



It appears to be, highly probable that the normal course of development is always as 

 I have described, namely that the "embryonic cells" of the Cypris larva, after entering the 

 crab at any point, are first carried to the upper part of the gut near the stomach, and then 

 grow downwards to the definite position of the adult, spreading out the root system meantime 

 in ali directions;. but it may well be that in abnormal cases the growth may proceed from 

 some other situation. 



However this may be, the youngest stages of Sacculina interna, which I have found, 

 have been always attached near or actually on the intestine at its upper portion immediately 

 below the paired diverticula which spring from the gut just below the stomach. Two such 

 Sacculinae are figured from the life in Piate 5 figs. 1 and 2. 



The gut of the crab in this region is separated from the external epithelium of the 

 crab by liver diverticula and blood spaces, and of course it is nowhere near the place where 



