TRANSACTIONS OF THE LINNEAN SOCIETY. 135 
never more than one individual is found in the same “ Nudi- 
branch, and this invariably occupies the same position, rest- 
ing upon the under surface of the liver-mass, and embracing 
two thirds of it with its long attenuated lateral processes. 
The under surface of the parasite is pressed to the liver; the 
anterior extremity forward, and the posterior extending as 
far back as the region of the branchial circle; here the two 
last segments of the body penetrate the skin of the Nudi- 
branch to which they are firmly attached.” “It is a remark- 
able fact, that this penetration and an attachment always 
takes place within the branchial circle; and consequently, 
the ovigerous sacs must float amidst the plumes, and be 
always exposed to the constant flow of water brought thither 
by the branchial cilia. 
- The males are more numerous and much smaller than the 
female, and generally several are associated with each 
female. ‘They always live immediately beneath the skin, 
either adhering to the viscera” or “the female’ They are, 
curiously enough for an internal parasite, furnished with an 
eye; the reason for which is explained by the circumstance 
that, as they undoubtedly enjoy a limited degree of loco- 
motion, they might lose themselves among the viscera, in 
the interior part of the body, had they not an organ which, 
however low in organisation, yet suffices to guide them 
towards the surface, immediately beneath the skin, where 
the female resides permanently. attached. The habits of 
S. brevipes appear to be very similar. 
Both species are “‘ remarkable for their great size, in com- 
parison with the animals they infest. S. gracilis is not very 
much shorter than the liver upon which it lies ;” whilst 
S. brevipes occupies nearly one third of the visceral cavity of 
D. coronata. The Nudibranchs, however, seem perfectly un- 
conscious of the presence of the insidious foe. 
II. The second paper is by Mr. Lubbock, being the first 
part of an “ Account of the Development of Chlocon (Ephe- 
mera) dimidiatum.” This account is preceded by some 
“Introductory remarks with reference to the number and 
nature of the changes undergone by Insects in the course of 
development from the egg upwards.” 
After referring to the “ opinion general among entomolo- 
gists, that we may observe four distinct periods of exist- 
ence in every insect, viz., those of the egy, the larva, the 
pupa, and the imago,” he observes that “these differences re- 
late only to what we see in insects after birth; while if we 
are to treat the question in a philosophical manner, we must 
