92 Dr. F. Miiller on Entoniscus Poreellanse. 



the soft membrane of this articulation, but carrying it in before 

 it. Thus, regarding this as residing in an inversion of the external 

 skin of its host, it might be called an external parasite, like 

 Bopyrus and other Isopods, although it buries itself between the 

 liver, intestine, and heart, and is entwined by the convolutions 

 of the seminal ducts. 



Not unfrequently there are two, and I once found even three, 

 Entonisci in the same Porcellana. 



Safely enclosed in the enveloping sac, the male of Entoniscus 

 does not require the sharp-clawed clinging feet of the male of 

 Bopyrus ; and the female has a sufficient security for the con- 

 jugal fidelity of her mate in his club-feet, which render it im- 

 possible for him to make an excursion into the open sea. 



With regard to the occurrence of this parasite, I have yet 

 one circumstance deserving of notice to mention, namely, that 

 Lernceodiscus and Entoniscus frequently occur on the same Por- 

 cellana. Having noticed this relation, and knowing well how 

 deceptive estimates of comparative numbers are without actual 

 counting, I kept a record of the parasites of 1000 Porcellana 

 examined between the 4th of July and the 1st of August. For- 

 tunately this investigation was facilitated by the circumstance 

 that Entoniscus also is recognizable from without, as, when the 

 tail is strongly bent back, the liver, or the ovaries, or the eggs 

 between the brood-leaves, or even the black eye-spots of the 

 young brood shimmer through the articulation behind the 

 sternum. Lernceodiscus occurred in 84, and Entoniscus in 49, of 

 these 1000 Porcellana ; hence we ought to find the two parasites 

 together in 49 x 84 in a million, or 4 in a thousand, whilst they 

 did occur together 21 times*, and therefore five times more 

 frequently than the frequency of each individual species would 

 lead one to expect. The explanation of this frequent common 

 occurrence, I believe, may be that Lernceodiscus prevents a close 

 approximation of the tail and sternum, and thus facilitates the 

 access of the young Entoniscus to the ventral surface of the 

 Porcellana. 



EXPLANATION OF PLATE II. figs. 8-16. 



Fig. 8. Entoniscus Porcellance, female, after the removal of the eggs from 

 the brood-leaves, magnified 1 5 diameters : e, ovary ; h, heart ; 

 I, liver. 



Fig. 9. Male: a, magnified 15 diameters; b, magnified 90 diameters; 

 h, testes ; /, liver; a, eyes. 



* In this neither the younger Entonisci not recognizable from without, 

 which afterwards occurred in Porcellance bearing Lernceodiscus, nor the 

 Porcellance harbouring Entoniscus and bearing only the golden coronet of 

 cast Lernceodisci, were counted. 



