J Q The Endoparasitic Development of the Rhizocephala. 



roots and gradually attaining to its definitive position on the intestine of the crab at the 

 junction of thorax and abdomen. 



Before describing these early stages I wish to give some directions as to the best 

 method of studying Sacculina interna, because, owing to the controversial nature of the 

 subject, it is probable that some naturalists would like to satisfy themselves as to the truth 

 of my statements. 



Since it is impossible in the great majority of cases to foresee which crabs contain a 

 Sacculina interna by mere inspection, it is advisable to attempt the study only where the 

 parasite is known to be very common. At KoscofF, according to Delage, Sacculina carcini is 

 very common, and Sacculina neglecta at Naples has been found by me to infect about an eighth 

 of the w'hoie population of Inachus scorpio. The following directions apply to Sacculina 

 neglecta at Naples. 



The first thing for the investigator to do is to thoroughly familiarize himself with the 

 living appearance of the roots of the Sacculina, so that he can at once recognize and distin- 

 guish these roots from all the tissues of the crab. This can be accomplished by the exami- 

 nation of the roots of an adult Sacculina externa. A large collection should then be made 

 of the crabs not bearing Sacculinae externae, but these crabs should be taken from an area 

 where Sacculinae externae are common. The most promising time of the year is the late 

 autumn and winter, and for preference young crabs of 5 — 16 millimeters carapace length 

 should be selected. The thorax of each crab, freshly killed, is now removed and pieces of 

 the liver surrounding the posterior part of the intestine are carefully removed and examined 

 under a fairly low power. 



If Sacculina roots are recognized the crab is infected with a Sacculina interna, and 

 the whole intestine should be very carefully removed and preserved. 



The central tumour containing the body of Sacculina at some stage of development 

 will be found attached to the intestine somewhere in the neighbourhood of the unpaired 

 diverticulum which springs from the intestine where the latter passes from the thorax into 

 the abdomen (see Plate 5 fig. 10a). The only satisfactory way of studying the organization 

 of Sacculina interna is by serial sections. If Sacculina roots are not recognized clinging to 

 the liver, in any particular crab, two alternatives are possible: either the crab is uninfected 

 or else the Sacculina interna is very young and has not yet established its system of roots. 



Carefully separate the liver tubes from the intestine along its whole length and examine 

 with a lens if there is anything clinging to the intestine on its upper portion immediately 

 below the stomach, or on its middle portion. If any body can be detected remove the 

 whole intestine along its whole length and examine this body under a low power. In 

 Mime cases blood clots and vessels are attached to the intestine which must not be mistaken 

 for the young Sacculina. In this manner after the dissection of a hundred crabs or so, one 

 or two Sacculinae internae will be found loosely attached to the upper or middle portion of 

 the intestine with a few short roots beginning to grow out into the surrounding tissues, but 



