46 



PROF. AGASSIZ 7 S 



and B), I have already shown the structure by 

 which the water is introduced into the cavity. In 

 the Echinoderms is figured this arrangement in the 

 star-fishes (Plate XXXVIII, fig. D). 



Through these almost microscopic tubes the 

 main cavity is constantly filled with water, which 

 escapes freely from the star-fishes when they are 

 taken out of the water. They should not be mis- 

 taken for ambulaesral tubes, which are placed in re- 

 gular rows whilst the water tubes are scattered 

 almost over the whole surface of the animal, but 

 only seen when fully expanded in the living ani- 

 mal. In the Actinia, the water system is plainly 

 developed (Plate XX, fig. D), in the forms of mi 

 nute pores arranged in vertical series. 



From the above statements it can be concluded, 

 that there is the strictest agreement between all 

 Kadiata in the general plan of their structure ; and 

 this analogy can even be traced in the embryonic 

 growth all the Radiata beginning by the formation 

 of a distinct layer round the yolk in the form of a 

 spherical crust, from which the more animated 

 parts are derived, whilst the alimentary cavity is 

 formed by the modification of the central mass of 

 yolk. In addition to this regular mode of repro- 

 duction, the Polypi and Medusae are also multiplied 

 by buds, and some of the Medusas by a peculiar 

 modification of the alternate generation new ind 1 

 viduals being formed by the transverse division of 

 a primitively simple stem. Whether anything like 

 an alternate generation takes place in the class of 

 Echinoderms, remains still doubtful ; but I cannot 

 help thinking that the Pedicellarice are the last in- 

 dications of a kind of budding, giving rise to very 

 low organisms, which can only be compared to the 

 peculiar beak-like buds of some of the Sertularise. 

 This uniformity of structure and growth calls for 

 an additional remark. Ever since the natural and 

 physical sciences of graphical representations have 

 been introduced, progress has been made much 

 more rapidly than before. 



As soon as Humboldt had drawn his isothermal 

 lines, investigations in all parts of the globe 

 were at once called for. And so it was in chemis- 

 try, when the formulae were introduced to re- 

 present chemical composition, by which an insight 

 into the constitution of numerous bodies could be 

 obtained at one single look. Now in the animal 

 kingdom nothing has yet been done to represent 

 by symbols either structures or natural affinities; 

 only the teeth of Mammalia are noticed in a regular 

 system. Something, however, has been done, and 

 is extensively introduced in Botany, to represent 

 the arrangement of the leaves of plants and the 

 parts of the flowers, by formulas. But to represent 

 structures to represent affinities by symbols is an 

 attempt which has not yet been made, and which I 

 think could now be satisfactorily introduced. Only 

 general symbols for the main groups of the animal 

 kingdom, representing their fundamental erabry- 

 ological character, have been Introduced into the 

 text book which I have published in connection 



with Dr. Gould, where a star was used to represent 

 the Radiata, where Mollusca when represented by 

 an inverted Greek W, Articulata by a W, and 

 Vertebrata by the figure 8, these diagrams having 

 reference to the peculiar mode of development and 

 of the germ. That the Radiata is best represented 

 by a circle, is shown by what I have said of the 

 first formation of the germ, wLich surrouuds the 

 yolk entirely from beginning, and forms, as ifi 

 were, an animal crust round the yolk, so that we 

 could have, instead of a star to represent Radiata, 

 any general simple circular outlines with a dot in 

 the centre, to remember the analogy of their gen- 

 eral structure with that of the eggs, with the low- 

 estcondition of all animals. 



[PLATE XXXIX ] 



But when we would like to represent special 

 classes, either,. Polypi, Medusas or Echinoderms, I 

 would propose that instead of a dot, we should 

 have for the Polypi a longitudinal line across the 

 circle, (Fig. B.) indicating the first apperance of a 

 bilateral arrangement under the form of a sphe- 

 rical circle. To represent the Madusae, I would 

 propose a circle with a cross within, (Fig. C,) to 

 indicate that in these animals there is a radia- 

 tion of branching tubes from the central cavity. 

 And to represent Echinoderms, I would have a 

 star in the circle, (Fig. D) corresponding to the 

 form which is the most characteristic of that class. 

 So that the three classes of Radiata would be 

 represented by their peculiar figures, and by the 

 addition of a single letter to these symbols, we 

 might at once represent either of their families 

 for instance, having the diagram of Echinoderms, 

 an additionrl C would represent Crinoids, E would 

 Indicate Echini, and A would represent Asterid 

 (Fig. E). 



And how important this would be, is at once ob- 

 vious, if we look at geological works, where the 

 lists of fossils, simply mentioned by their names, do 

 not convey any idea to the reader. But if, instead 

 of Saccocoma, shortly we append the figure of 

 Echinoderms, and add aC, we should know at first 

 sight that this is a fossil of the class of Echino- 

 derms belonging to the family of Crinoids, and the 

 symbol itself would at once remind us of the pecu- 

 liar structure of these animals. Those great fig- 

 ures being used to indicate the families, an addi- 

 tional small letter might indicate minor divisions, 

 and so on ; so that these symbols would show all 

 the affinity of any given animal, and form in real- 

 ity a complete picture of the various relations 

 which exist among all animals. 



In my next Lecture, I shall enter into the depart- 

 ment of articulated animals. 



