168 Papers from the Department of Marine Biology. 



of the invertebrate animals of the deep sea, due possibly to the fact 

 that the red rays from the sun are rapidly absorbed as they penetrate 

 into the depths of the ocean, so that at depths greater than 1,000 

 fathoms there is practically no red light, and here red-colored animals 

 must appear black and be well concealed in the general darkness of 

 their abysmal realm. The Coronatse are characterized by having a 

 deep ring-like furrow cutting into the thick wall of the sides of the um- 

 brella; and peripheral to this are gelatinous thickenings in the radii 

 of the tentacles and sense-organs. The gelatinous wall of the bell is 

 much reduced in thickness at the ring-furrow, the thin part acting as a 

 hinge to permit the creature to close its bell during contraction. These 

 forms are common in the deep waters of the Philippines, as indeed they 

 are upon the bottom of all seas 500 fathoms or more in depth. Most 

 of the species, such as Atolla and Periphylla, do not normally come to 

 the surface, but a closely allied form, the little Nausithoe, is one of 

 the most universally distributed surface forms of all warm seas, while 

 the mature Linuche occur in vast numbers, all rapidly pulsating and 

 resembling little brown thimbles, the swarm often covering square 

 miles of ocean in tropical regions. 



IV. The Semceostomata are the common large jelly fishes of our coasts, 

 such as Aurellia, Cyanea, and Dactylometra. They have tentacles and 

 a single cruciform mouth provided with veil-like lips, and there is no 

 ring-furrow cutting into the surface of the umbrella, such as is seen in 

 the Coronatse. They are common in bays and brackish estuaries and 

 are the largest and most conspicuous of all jellyfishes in temperate 

 regions. 



V. The Rhizostomce are the large jellyfishes of the East Indian and 

 tropical seas, where they are commonly as conspicuous as are the 

 Semaeostomese in our cold northern waters. They have numerous 

 mouths and no tentacles, and their gelatinous substance is often as rigid 

 as newly formed cartilage. Often they occur in swarms in the harbors, 

 swimming strongly against the tide, and after a storm great numbers 

 are found stranded upon the shore. The rigid gelatinous substance of 

 these jellyfishes is very characteristic and was seen in fossil forms found 

 in the Jurassic lithographic slates of Steinheim in Bavaria, showing that 

 in the age of the Reptiles these most highly differentiated jellyfishes 

 existed. Indeed, so old are the jellyfishes that their relationship to the 

 echinoderms, sponges, and ctenophores remains unknown all inter- 

 grading forms, if such ever existed, having died out long ago, as is often 

 the case in very ancient orders. 



In an early stage of development the higher animals commonly pass 

 through a condition in which they have only an outer cell-layer and a 

 cavity lined by cells destined to form the intestine. Theoretically 

 speaking, they are simply little 2-layered sacks, the outer layer being 

 the external skin with its nervous and sensory organs, and the inner 



