382 IV. C. M' INTO SB [may 



2. Phenomena of histolysis without external meta- f Clistomastiis lineatus. 



morphosis, but with scissiparity . . . {Palolo viridis. 



3. Phenomena of histolysis, accompanied by ex- f TT M 



ternal metamorphosis (epigamy or epitokousl p. . ,., 

 condition), and sometimes by scissiparity) Q ,,., 

 (schizogamy) [bylndae. 



They point out the comparative frequence of the epitokous condition 

 in the annelids, and, moreover, that the phenomena of histolysis asso- 

 ciated with sexual maturity is very general in the group. Thus there 

 is a close parallelism between them and certain fishes, for instance the 

 salmon, as ably shown by Miescher of Basle, and Noel Paton of 

 Edinburgh. 



The fourth chapter of the paper is devoted to a consideration of the 

 various adaptations of annelids for a pelagic life — in order to ascertain 

 what connection the temporary pelagic condition at sexual maturity 

 has with a completely pelagic life. Pelagic annelids may be grouped 

 (1) into those only pelagic at sexual maturity, (2) pelagic larval forms, 

 (3) those permanently pelagic. 



Epitokous annelids fall under the first category, and in some their 

 existence is brief, as, for instance, in the case of Palolo, which gives 

 an example of pelagic agony rather than a pelagic existence. On the 

 other hand, Exogone survives the period of reproduction, and sheds its 

 pelagic bristles. 



Most annelids, whether errant or sedentary, have pelagic larvae — 

 generally with long pelagic bristles^and the authors quote Haecker to 

 the effect that these long bristles are not only organs for locomotion, 

 but aid the animal in hovering and other movements. There can also 

 be little doubt that these bristles are — in such as the larval Spionidae 

 — protective, and are used by the larvae very much as the Polynoidae 

 use their bristles when attacked. 



The third group, viz., permanently pelagic annelids, is characterised 

 by the transparency of their tissues, large eyes, delicacy and length 

 of bristles. Certain Phyllodocidae, the whole of the Alciopidae, the 

 Typhloscolecidae, and the Tomopteridae (devoid of ordinary bristles) 

 are examples. 



The authors conclude that it must at present be admitted that 

 adaptation for a pelagic life may take place independently of the 

 epitokous condition. Indeed, it would have been well if the authors 

 had attended to cases, e.g., the Leeches and Nemerteans, in which 

 active pelagic habits can be assumed without a trace of bristles, and 

 in which the habits are not associated with reproduction, and not 

 always with a permanently pelagic condition. It is the muscular 

 system rather than the bristles which is mainly concerned, and it 

 does not follow that long delicate bristles are better fitted for 

 swimming than for hovering in the water. 



The last short chapter contains remarks on viviparity amongst 



