BRITISH NEMERTEANS, AND SOME NEW BRITISH ANNELIDS. 399 



resemblance between Ommatoplea and Borlasia (to take, for example, B. olivacea), 

 but the moment the ova pass from the animal, and the condition in which they 

 do so. a decided divergence occurs. Instead of being deposited as free circular 

 bodies, the products are here placed within a flask-shaped membrane, with one 

 end narrowed to a fine point, and the whole enclosed in a tough covering of 

 gelatinous mucus, which is fixed either to stone or glass, in the form of a bulky- 

 cord, as noticed by CErsted* When a female specimen is about to deposit ova, 

 she seeks the water-line, or a space above it, and quietly settles along the vessel. 

 By-and-by a copious exudation of tough translucent mucus takes place, which 

 envelopes the entire animal. In this mucus, which when fresh is crowded with 

 small ovoid granular corpuscles from the cutis, the ova are deposited in the flask- 

 shaped capsules, each of the latter corresponding to an ovary, and containing all 

 its ova, viz., from one to seven. Hence, by the nature of the parts, the ova are 

 arranged in a somewhat irregular double row along each side, the extremities 

 of the cord — corresponding on the one hand to the head and oesophageal portion 

 of the digestive tract, and on the other to the extreme tip of the tail — being free 

 from ova. In some instances, the posterior end of the animal was curiously 

 frilled and grooved on the ventral surface during deposition. When newly depo- 

 posited the mucus is softer and less tenacious than it afterwards becomes, and the 

 same may be said of the membranous flasks. The solidifying of the mucus is 

 analogous to what takes place, under similar circumstances, in the egg-capsules 

 of certain mollusca, e.g., Buccinum undatum and others. If one end of the 

 animal be disturbed from its original site on the glass before the ova are all 

 deposited, four rows will be found there instead of two, for sufficiently obvious 

 reasons. The ova of B. olivacea are of two shades, viz., white and pale- 

 brownish ; and though the dark-greenish examples often lay white eggs, they do 

 not seem to do so always. Each ovum measures from ^th to ^V*h of an inch 

 in diameter. The deposition takes place in January and February in those 

 long confined ; but some specimens sent from the St Andrews rocks towards the 

 end of April likewise deposited ova, so that some latitude in regard to date is 

 necessary. The American examples deposited their ova in January, and those 

 from Cuxhaven in March ; but the Nemertes communis of M. Van Beneden only 

 did so in September. It is often observed that impurity of the water causes 

 recently captured animals to lay their ova rapidly, as if from a kind of abortion. 

 The development of the ova in Borlasia obscura — a species apparently identi- 

 cal with our B. olivacea— has, been described by E. Desor| up to the period of 

 the extrusion of the young from the capsules; and Max SchultzeJ and Krohn§ 

 have also investigated the subject, especially the former, so that I shall only 

 dwell on such points as have not been elucidated. Our British forms seem to 



* Entwurf einer Syst., &c, p. 25. f Boston Jour. Nat. Hist. vol. vi. No. 1, 1850. 



+ Zeitch. fur wiss.'Zool. bd. iv. 1853. § Archiv fur Anat. 1858. 



