424 M. Leuckart on the genus Sacculina. 



not to have been acquainted with the labours of his prede- 

 cessors; he enters into no discussion of the systematic nature 

 of the parasites observed, but remarks that the pit by which they 

 are attached is probably to be regarded as the mouth, and the 

 second free opening (mouth according to Rathke) as the anus. 



I am happy that it is in my power to add to the preceding 

 observations, made known by Steenstrup, another, made in 

 the year 1836, which is the more important as it reposes upon 

 a perfectly natural notion of our animals, and also introduces 

 them into the system under the generic name of Sacculina. The 

 observation is due to Thompson, whose numerous important 

 discoveries have, singularly enough, nearly all been destined to 

 remain for a long time unnoticed, and to fall into almost com- 

 plete oblivion. Unfortunately, I know the memoir of our au- 

 thor (which was published in the ' Entomological Magazine/ 

 iii. p. 452) only from Wiegmann's ' Jahresbericht ' (1837, 

 p. 248), in which, however, it is treated with a certain degree 

 of mistrust. I learn from it that Thompson observed on the 

 abdomen of Carcinus Mcenas a new parasitic Crustacean " be- 

 longing to the Lernaeadse," which hung down by a neck-like 

 process between the membranous interstices of the tail of the 

 Crab, " like a bilobed leathern bag." From the wide orifice a 

 granular substance was pressed out, which, under the micro- 

 scope, proved to be a mass of larvae, " resembling those of Ler- 

 naocera *." 



So far the report. It is unmistakeably the Peltogasler Car- 

 cini that is here described; and there is no doubt that this ani- 

 mal, from the form of its larvae, its mode of life, and habitus, 

 belongs to the Lernteadte, although the circumstance that the 

 larvae are excluded within the body of the mother must certainly 

 be regarded as a remarkable departure from the other animals 

 of this group. Consequently, if we restore the name Sacculina 

 either for Peltogaster in liathke's sense, or at least for the form 

 characterized by Diesing as Pachybdella, we are only discharging 

 an old and almost superannuated debt. 



That Thompson's view was perfectly correct, has also sub- 



* Thompson docs not regard his Sacculina as belonging to the Ler- 

 ncpadte, but says " that it agrees with no tribe of the Crustacea;" and, from 

 his remarks, he seems to think that its nearest affinity is with Cirripedes. 

 He compares the larva with Argulus armiger of Latreille, a microscopic 

 Crustacean discovered by Slabber. He appears also to regard the Saccu- 

 lina as hermaphrodite, saying that its body is "entirely filled with the 

 ovaria, and an enormous testicular gland." His ovaria evidently corre- 

 spond with the organ described in the text as the " brood-chamber," and 

 his " testicular gland" is evidently identical with the cordate body described 

 by Leuckart as containing the true ovary and cement-gland. — W. S. 1). 



