M. Sars on the Development of the Annelides, 187 



his eyes. I therefore refer to his observations, as probably the 

 further development of our young Polyno'e takes place in a coin- 

 cident manner. 



The results of the above observations are briefly as follows : — 



1. Polyno'e ciyrata propagates in the months of April and 

 March by ova which are secreted from particular apertures on 

 the dorsal side in masses connected together by mucous fila- 

 ments ; they collect on the back and under the branchiae of the 

 mother, where they remain during their further development 

 and until the exit of the young. The branchiae have here there- 

 fore a similar function as in the freshwater Mollusca ( UniOf Ana- 

 donta), that of protecting the brood. 



2. The young when they leave the egg have a very different 

 form from that of the mother and a very imperfect structure. 

 They are short, oval, cylindrical, unarticulated, and so to say, little 

 more than mere head, for this occupies more than half of the en- 

 tire body, and has two very distinct eyes (the full-grown animal 

 has, as is well known, four). The mouth is a horizontal fissure 

 on the ventral side of the body, and the anus is situated at its 

 posterior extremity. With the exception of a circle of cilia, which 

 surround horizontally the centre of the body and effect locomo- 

 tion, there exist no other external members, no tentacula or an- 

 tennae, no feet with their appendages of cirrhi and bristles, and no 

 branchiae. All these organs must therefore be developed sub- 

 sequently, when the true body (abdomen) has grown and become 

 divided into articulations (as the observations of Loven show), as 

 well as the two eyes, which are still deficient, while the ciha, as 

 transitory, disappear. In short, we have here all the criteria of a 

 metamorphosis, — different external form, parts which disappear 

 entirely, and numerous organs which are subsequently added. 



It is therefore certain that many Annelides undergo a very 

 considerable metamorphosis. In this respect they are related to 

 the other Articulata, and indeed most to the Myriapoda, whose 

 young, according to the observations of Waga and Newport, leave 

 the egg in a very imperfect state and without any articulated 

 members. 



As connected with this subject, I must mention the mucous 

 globules which are likewise met with in the months of Fe- 

 bruary and Mai'ch on our coast, adhering at the depth of some 

 feet to Zostera marina and Fucus vesiculosus. These globules 

 (fig. 20) are about an inch in diameter, of a beautiful grass-green 

 colour, and consist of an immense number of eggs (b b) enveloped 

 in a tenacious mucus which is rolled irregularly like a riband 

 into a knot, the whole of which is coated with a slimy envelope. 

 The eggs are globular, filled with limpid chorion, somewhat al- 

 bumen, and grass-green yolk, which I observed in all the various 



