ANDROGYNOUS MOLLUSCA. 367 



found the same modified by the site to which it was attached, 

 so as to have become like a riband fully eight inches in 

 length and -f$ ths of an inch broad ; and this was elegantly 

 wrapped round the lower part of the stem of the Tangle, to 

 which it adhered by one margin only. The riband was of a 

 white colour, and within its substance the ova, in countless 

 numbers, were neatly arranged in regular cross spiral lines.* 

 The spawn of the Eolis papillosa forms an elegant spiral 

 chain of a milk colour and several inches long, twisted upon 

 itself and constricted at regular intervals, so as to resemble 

 a necklace made of bugles. The ova, as in the dioecious 

 phytophagous Mollusca, are very numerous. Mr. C. Darwin 

 calculated those of a Doris native of the shore of the Falk- 

 land Islands. " From two to five eggs (each youths of an 

 inch in diameter) were contained in a spherical little case. 

 These were arranged two deep in transverse rows, forming a 

 riband. The riband adhered by its edge to the rock in an 

 oval spire. One, which I found, measured nearly twenty 

 inches in length and half in breadth. By counting how 

 many balls were contained in a tenth of an inch in the row, 

 and how many rows in an equal length of the riband, on the 

 most moderate computation there were six hundred thousand 

 eggs. Yet this Doris was certainly not very common ; al- 

 though I was often searching under the stones I saw only 

 seven individuals." -j- This is a striking illustration of a fact 

 very general amongst invertebrate animals, their numbers 

 bear no proportion to the exceeding multitude of their eggs, 

 as if the law given to man to plenish the earth was in them 

 restricted merely to the perpetuation of the species. 



The terrestrial genera are greatly less fertile in ova. The 

 Helix pomatia, according to Lister, deposits only about 

 fifteen eggs ; and in our common snails they do not exceed 

 from thirty to fifty. In general they are separated from 

 each other, though deposited in little heaps ; but a large 

 species of native slug which inhabits cellars has the eggs, 



* There is a figure of the spawn of a Doris in Baster, Opusc. Subs. i. 

 tab. x. fig. i. C. D. The spawn of Pleurobranchus is very similar. Audouin 

 and M. Edwards, Litt. de la France, i. 134. 



t Voy. Adv. and Beagle, iii. 258. The ova of Doris tuberculata, "on 

 a moderate computation, cannot be less than fifty thousand." ALDER and 

 HAISTCOCK in Ann. and Mag. N. Hist. xii. 235. But its young Ct have myriads 

 of enemies in the small infusoria, which may be noticed with a powerful 

 microscope hovering round them, and ready to devour them the instant 

 weakness or injury prevents their keeping in motion the cilia, which serve 

 both for locomotion and defence. Let them cease to move, a regular attack 

 is made and the animal is soon devoured ; and it is interesting to observe 

 several of these scavengers sporting in the empty shell as if in derision at 

 the havoc they have made." PEACH in Ann. and Mag. N. Hist, xv, 446. 



