Gonads of Arenicola 73 



feature in a dissection of this species. In the female the gonad is 

 produced into processes, which at first are few, small, and more or 

 less conical in shape, but later on increase in number and size, and 

 in maturing examples assume very large proportions (PL XV, Fig. 52). 

 Such processes are packed with numerous oval oocytes, about 12 mm. 

 in diameter, each with a thick vitelline membrane. In male specimens 

 the gonad bears one, two, or occasionally three or four, thin reniform 

 outgrowths, pink, grey or milk-white in colour, according to the 

 condition of their contents (Fig. 53). Within each of these out- 

 growths, which may attain a length and breadth of 6 and 4 5 mm. 

 respectively, are present male cells in all phases of development up 

 to almost ripe spermatozoa. In this species, therefore, the repro- 

 ductive products are retained in association with the gonad to a 

 much later stage of growth than in the other species of the genus. 

 Just before the breeding period, the envelope of the gonad is 

 ruptured, and the sexual products fall into the coelum and there 

 undergo their final stages of growth. 



The genital products, in all the species of Arenicola, escape from 

 the coelom to the exterior by way of the ncphridia, 1 the vesicles of 

 which are often found, during the breeding season, strongly distended 

 with ova or sperms which have accumulated therein preparatory to 

 discharge. 



DEVELOPMENT. 



Max Schultze 2 found on the island of Neuwerk, off Cuxhaven, 

 large numbers of castings of Arenicola marina, and near to many of 

 them a pyriform, greenish-yellow, gelatinous mass, about half an inch 

 in length, fastened into the sand by a gelatinous stem about two 

 inches long. He traced the development of the eggs within these 

 masses, which he regarded as the egg-masses of the lugworm, an 

 opinion shared by a few subsequent writers. Messrs. Cunningham 

 and Eamage and Profs. Ehlers and Fauvel ascribed these egg-masses 

 to Scoloplos armiger, and Dr. Groot 3 has definitely proved their 

 parentage by finding them in an aquarium in which specimens of 

 S. armiger, but no examples of Arenicola, were living. 



1 M. Bohn states that the ova escape by perforations, due to histolysis 

 of the body-wall at the breeding season (C. R. Acad. Sci. Paxis, cxxxiii (1901), 

 p. 647). The present writer has not observed this phenomenon in any of the 

 numerous ripe examples which havelpassed through his hands. 



2 Abh. naturf. Ges. Halle, iii (1856) p. 216. 



3 Proefschr. Univ. Leiden (1907), p. 23. 



