78 PROGRESS OF MICROSCOPICAL SCIENCE. 



the gills have all disappeared. The time consumed in this wonderful 

 process is a little over one hundred days. 



The Affinities of Crinoids. — Professor Agassiz gives the following 

 account of Herr Metschnikoff's recent researches on these animals. 

 He quotes from the ' Bull. Acad. St. Petersburg,' p. 508, February, 

 1871. The researches are of considerable importance, as they throw 

 new light on the affinities of the Crinoids. Thoroughly familiar, 

 says Prof. Agassiz, with the Pluteus of Holothurians, Echini, Star- 

 fishes and Ophiuraus, Herr Metschuikoff commenced tlie investigation 

 of their earlier stages with the determination of tracing the presence 

 of the peculiar water-system of the larvae of the other orders of 

 Echinoderms, what had been previously written by Busch, Allman 

 and Thomson, on the early stages of Comatula, giving no data what- 

 ever bearing upon the subject. To his surprise he found no such 

 water-system, nor could he trace anything in any way homologous to 

 it ; he also discovered that what constitutes the water-system of adult 

 Crinoids, which has always been homologized with the water-system 

 of other Echinoderms, is developed in a totally different manner. In 

 the free-swimming Comatula larva the bag-like digestive sac is the 

 only organ developed, it becomes the digestive cavity of the adult 

 after the larva attaches itself to the ground. He noticed the tentacles 

 as diverticula of the digestive sac in the interior of the larva ; these 

 subsequently force their way through to the exterior, at the time when 

 the digestive bag has become further diiferentiated, and is provided 

 with a mouth opening in the centre of the oval disk, and an anus 

 opening not far from it on the side of the calyx. There is formed at 

 this stage a large cavity which divides into two parts ; the upper 

 part, uniting the hollow tentacles at their base, forms the so-called 

 circular canal, while below it, and connecting with it, we have a large 

 cavity forming the perivisceral cavity, a mode of development of the 

 circular ring and of the perivisceral cavity totally unlike that observed 

 in Ophiurans, Starfishes, Echini, and Holothurians. Metschuikoff 

 compares the mode of development of the upper and lower cavity to 

 analogous processes in the embryonic growth of Alcyonella and other 

 Bryozoa ; he traces a striking similarity in the structure and position 

 of the digestive organs and tentacles with similar organs of Bryozoa. 

 However that may be, he has shown conclusively that the larva of 

 Comatula has apparently nothing in common with other Echinoderm 

 larvae ; but, says Prof. Agassiz, we must wait for his figures on this 

 intricate subject before we can decide if the position he assigns to 

 Crinoids is true to nature. 



Monocotyledons the Type of Seeds. — A paper on this subject having 

 been read by Mr. Thomas Meehan before the American Association 

 at its last meeting. Dr. T. C. Hilgard made the following remarks upon 

 it. He observed that the whole question came back to the laws of 

 phyllotaxy . The very fact of these " genetic " nurftbers, as he had 

 called them, required the second element to be derived from the first 

 one ; as all radial organs must be derived from their predecessors. 

 The fact itself was apparent in the far-too-much neglected phenomena 



