ARIOW ATER. 171 



constituted by a tricuspid median tooth, flanked by about twenty-six rows of lateral 

 teeth, which though obscurely tricuspidate adjoining the median row, gradually 

 become distinctly bicuspid ; the marginal teeth are mainly bicuspid ; the mesocone 

 increasing vastly in size and importance, the endooone totally disappearing, and the 

 eotocone diminishing greatly until in the extreme marginals it also becomes totally 

 lost, and the teeth are simply aculeate. 



The formula of a Dublin specimen, collected by Mr. J, R. Reddino-, is 

 ii + 14 + 1 + l-l + l-^T X 160 = 9,760. 



Reproduction and Development. — The congress of this species is 

 preceded by the prolonged circular procession pre- 

 viously described, and which may be continued for 

 an hour or more, the head of each animal resting 

 upon the tail of its partner during the promenade, 

 and both slowly devouring the mucus exuded by 

 the caudal gland and by the body cells. The con- 

 gress is not of long duration, the union being 

 effected by the extrusion of the genital cloaca, 

 especially of the oviduct, etc., which constitute 

 the intromittent organ, the seminal element being 

 mutually transferred by means of the denticulate 

 spermatophores. ^ on, c 



rrn ■ • 1 • '^"^' 201.— Sperraatophore 



This species, however, sometimes reproduces of a. aier v. ra/a, enlarged 

 parthenogenetically, as Mr. F. W. Wotton has "'*'""' 



reared individuals in captivity, which though kept strictly isolated almost 

 from birth, produced fertile eggs. 



The eggs, which are excluded in from four to five weeks after the union 

 has taken place, are about five mill, long, and four mill, in diameter, some- 

 what oval in shape, thick skinned, and semipellucid when fresh, but quickly 

 chaiiging to an opaque-white, a circumstance ascribed to the innumerable 

 calcareous particles in the outer envelope, this calcification tallying with the 

 copious deposit of lime in the arterial walls. They are deposited in vast 

 numbers at almost all seasons of the year — many clusters have been found 

 as early as January in this country— under stones, old wood, dead leaves, 

 at roots of plants, etc., usually in clusters of from twenty to fifty, or more; 

 they hatch in from thirty to fifty days, according to the weather. 



The young when hatched are usually unicolorous, but apparently vary 

 in shade, in different countries ; in Germany, Scandinavia, and North 

 Central Europe they are said to be pale yellow or greenish-white, but 

 more inclined to blackish in the mountain regions, while in the warm 

 plains and in the south they are reddish, and in England frequently of a 

 yellowish or greenish-grey, with slightly darker shield and head, often closely 

 conforming in tint to the fallen faded leaves of autumn. In many cases lateral 

 banding develops during growth, which may occasionally, especially near 

 the outskirts of its range, persist in adult life, but usually the darker 

 markings become clouded over and the unicolorous stage is reached. 



Mr. W. A. Gain has carefully chronicled the varied changes undergone 

 by animals during growth. At eighteen mill, in length they were almost 

 without exception of a greenish-yellow tint, with greyish lines and mark- 

 ings, but this in some cases would gradually but quickly change to a 

 brownish tint, the tint gradually becoming a rich brown with dark lateral 

 bands on body and shield, and eventually when full grown presenting a 

 deep brown back and shield, with black-brown sides and orange fringe. 

 Other specimens, apparently quite similar when young, may become very 

 differently coloured as adults. 



