146 MARINE BIOLOGICAL LABORATORY. 



Speaking in general we may say that prior to 1880 

 the group was placed either amongst the Arachnids 

 (spiders, scorpions, etc.), or else amongst the Crustacea. 

 Recent work has shown Crustacea to be out of the 

 question, I think, but at the same time, the alternative 

 was not believed to be the Arachnids. The group has 

 been independently monographed by Dr. Hoek in a 

 report of the Challenger Expedition, and by Professor 

 Dohrn in a volume of the Naples Fauna and Flora. 

 Each of these authors concludes that we are to believe 

 the group to have arisen, independently of other Arthro- 

 pods (Crustacea, Spiders, Insects), from the Annelids. 

 While their work has been very complete as regards 

 the adult anatomy, and inasmuch as any speculations 

 about the inter-relationships of animals must take into 

 account largely the adult structure, yet there remained 

 unworked another equally valuable source of knowledge; 

 viz. the study of the changes which the animal under- 

 goes in its development from ^gg to adult. Information 

 from this source must take equal rank at least with 

 that from adult anatomy and histology, and may throw 

 light upon hidden relationships which could not other- 

 wise be obtained ; and I wish to give hurriedly a few 

 facts about the embryology of these animals, choosing 

 those which seem to me to bear directly upon the re- 

 lationship of the Pycnogonids to another group to which 

 a study of the development has led me to believe the 

 sea spiders to be allied. 



Without a series of figures to illustrate these stages 

 of development, it will be impossible to do more than 

 merely mention, in the briefest possible way, those points 

 which are to be used in our comparison. Moreover, 



